Evidence for New Zealand:

The disputed try against Wales, extracted from 1.

Here is a statement made by Robert Deans in a telegram sent to The Daily Mail (London) the day after the match: -
" Grounded ball six inches over line some of Welsh players admit try, Hunter and Glasgow can confirm was pulled back by Welshmen before Referee arrived Deans."

Mr. J. A. Buttery, The Daily Mail (London) correspondent, writing of the match, said:
" It was now that Wallace chafing under the prolonged inaction which the Colonial three-quarter line had endured, rushed with the desperation born of despair into the thick of the fray. . Gathering the ball from an opponent's toe, he tore his way through every obstacle, and in a trice was speeding down the field, with Deans on his flank, and only two opponents to pass. It looked an absolutely certain try. Winfield went for Wallace a dozen yards from the line, but ere he could reach him the ball had been passed out to Deans racing down the touchline. He, too, was collared, but not before he had grounded across the Welsh line, though the referee -whose decision is bound to be accepted in such matters declared that he had been 'held up,' and ordered a scrum instead of a place-kick."

The foregoing is taken from Why the All Blacks Triumphed (Daily Mail). .
Said the late Mr. G. H. Dixon, the manager, in his book, "The Triumphant Tour o of the New, Zealand Footballers, 1905 .
"Again Wallace, picking up on his own side of the half way, made a brilliant dodgy run, and passed to Deans, who dived over and grounded the ball well over the chalk mark. He was at once dragged back. That this was an absolutely fair try there is overwhelming evidence, and it was most unfortunate that the referee should not have been on the spot to see what actually occurred. To sum the game up, I am of the opinion that on the day, New Zealand did not deserve to win, but that they actually made a draw of it I am certain."

By " Major," in The Sportsman:
" I was within six yards of the spot when the New Zealanders scored the disallowed try. It was the unanimous verdict of a goodly number of Welsh supporters next to me, and also my own, that no fairer try has been scored on the football field. I readily concede that on the day's form the better team won, but the legitimate result should unquestionably have been a draw."

Six years after the Welsh match the great English critic, Mr. E. H. D. Sewell, published The Book o of Football, which contained the following: -
" Many people will remember the terrific struggle at Cardiff Arms Park when both Wales and New Zealand scored a try each, but that of the latter wasn't counted good. It was more of a struggle than a game of football, and for the first time the New Zealanders showed they were human and possessed nerves. The affair will always be remembered by me for the perfect full-back play in the matter of accurate catching and kicking of H. B. Winfield, the dash of Teddy Morgan, the stupidity with which the New Zealanders punted in his direction, and the mercilessness, amounting almost to ferocity, with which J. D. Dallas of the Watsonians penalized Gallaher ... I have often been asked whether they were stale when they reached Wales, and have no hesitation in stating that Welshmen never saw the real New Zealand team."

Finally, W. J. Wallace published his memoirs in The New Zealand .Sportsman (Wellington) in the middle 'thirties, quoting:
" A line out had been formed on our side of half way, and from a long throw-in the Welsh forwards gained possession. Freddy Roberts was just in front of them, and in order to beat him they made a diagonal kick, but just a little too hard. I was on the wing on the touch-line and I dashed in, scooped up the ball in my stride, and cut across the forwards before they could lay hands on me. I then made diagonally across the field until I came in front of Nicholls. In order to beat him I turned and straightened up and when he came at me I side-stepped him and slipped through between him and Gabe so that I had a clear run through to Winfield, the full-back who was standing about tile twenty-five yards line. Meanwhile Bob Deans had scented the possibilities of the situation and had run his hardest to come up in support. As I neared Winfield I was undecided whether to kick over his head or sell him the dummy and then I heard Bob calling out: 'Bill, Bill.' I feinted to pass and could have gone through on my own, for Winfield took the dummy, but quickly recovered himself and came at me again. Rather than risk any mishap at this critical stage I threw Bob Deans out a long pass which he took perfectly and raced ahead. But he made a slight mistake here, for instead of going straight ahead he veered in towards the goal-posts. Teddy Morgan, the Welsh wing three-quarter, was coming across fast from the other wing and Bob was becoming a little exhausted. Bob saw Teddy Morgan in time and altered his course to straight ahead and just grounded the ball six inches over the line and about eight yards from the goal-posts as Teddy dived at him and got him round the legs. But the try had been scored. It is only fair to the Welshmen to say that they were great footballers. Some of them quite openly stated that the result was wrong and that beans scored a try that should at least have made the scores level. On his return to Guy's Hospital, after the game, Teddy Morgan told Dr. P. F. McEvedy that Deans had scored a fair try and he still sticks to that through the passing of the years. At the dinner after the Welsh match in 1924 he was sitting alongside Cliff Porter and he asked Cliff if he knew me . . . Morgan said then that Deans scored a fair try and Cliff got him to write it on a menu card. If the man who collared Bob Deans says that Bob scored, what more evidence is needed? "

Evidence for Wales:

The 1905 All Blacks Tour of Britain - Paper by: Gareth Williams University of Glamorgan (mainly about the game against Wales)

From RugbyRelics.com:

The game continued with both teams capable of scoring, the closest opportunity came for the All Blacks when three-quarter Bob Deans was brought down inches from the line. Deans maintained until the day he died that he had scored on the day and the Welsh try scorer Teddy Morgan years later agreed. Morgan also claimed to have brought Deans down but the 'honour' of the try saving tackle fell to Rhys Gabe. Gabe recalled the incident in an article prior to the 1963 match.

• "It was then that Deans figured in the controversial "try" episode. Wallace, a superb runner on the wing, broke away. He was challenged by our wing, Willie Llewellyn, and passed inside for Deans to fasten on to the ball and burst for the line. It was a moment of high tension and I put all I knew into a sprinting effort to catch the flying All Blacks' centre. I came up with him going at tremendous speed and crashed him to the ground from the side. I knew it was touch and go whether I had managed to tackle him before he reached the line then, as I lay there gripping him firmly, I felt Deans trying to struggle away from me. Instinctively I clutched tighter. Then I realised why he wanted to wriggle on. He had not reached the line. He was just inches short. I pulled back with all my strength and then the whistle went. The referee had arrived on the spot, Deans was still in possession of the ball and our goal-line was just beyond his reach. There was no other real chance for the All Blacks 

Deans claims he was pulled back, but it is difficult to see how a prostrate 11st 9lb Gabe could have pulled back 13st Deans if as the Canterbury man stated he had crossed the line. The referee, John Dewar Dallas (1 cap for Scotland in 1903) is said to have been too far away but in a letter following the game he states that he saw the incident quite clearly and that Deans was brought down 6 to 12 inches short of the goal line. 

References:

1. History of New Zealand Rugby Football - A.C.Swan 1870 - 1945, Pub. 1948 by New Zealand RFU by A.H. & A. W. Reed, Wellington.

2. The 1905 All Blacks Tour of Britain - Paper by: Gareth Williams University of Glam organ