I think that would set a dangerous precedent, estimating how many sneaked in. Nobody will ever know how many were there, and as it's over 50 years ago, I don't think anything would be gained anyway, except depriving Australia of something.
If we did want the record back we can have it. The Australian record was for two matches, so at anybodys guess probably some of the spectators for the first game went home before the 2nd, and some of the second games speccy, probably didn't turn up for the first, so in effect their record means that there wasn't that number in the stadium at any one go, Halifax v Warrington means there was only 1 game, therefore the recored for a single matchs attendance is still the UK's