Not sure about 'new' Tank in terms of when it was taken compared to the first appearance of the tanks as appears to be a Mk IV Male with the sponson pushed in
It does appear to be a Mk IV, definitely a male and not a supply tank. I do note, however, that the stowage box is missing from the rear roof panel; were late Mk IIIs given the external fuel tank? I don't recall at present exactly whether or not I have read that the last Mk IIIs were so fitted - anyone else know if it could be a late III?
I know Mk IIIs don't have these things, but since they did gain new sponson designs mid-production, I was unsure whether I had read that very late examples were virtually Mk IVs, because of new bits being introduced bit by bit into the production line. It's new to me to see a IV with no stowage box on the roof - could it have been missing from the first examples? Also, have just noticed that it seems to be lacking the upper spaced-armour plate at the back - perhaps the bottom one behind the fuel tank as well.
The smaller Mark III Female sponsons are quite different to the Mark IV Female sponsons. The Mark III type don't fold inwards like those of the Mark IV. Consequently the Mark III sponson has lifting lugs that the Mark IV doesn't need. Also, the Mark IV sponson has a double run of rivets around it's upper edge whereas the Mark III has only a single line of rivets.
Early Mark IVs didn't have the spaced armour. Agree the missing stowage box is unusual but it's not unique.