any help would be appreciated. After much grunting, skinning of knuckles, dirt in eye and petrol down sleeve I have now finally managed to remove the old tank ready to fit the new one. However I notice a very slight difference, next to the bigh hole where the sender unit fits in, is a smaller hole for the pipe from the fuel pump. However on the new tank this hole does not exist. It's not just a drilled hole either, it has some type of reinforcement on the inside of the tank for the screws to fit into.
Any ideas?

Looks like the later tank type has the fuel feed pipe integrated into the sender unit. You either need the earlier tank or the later sender.