Hmm, are you saying the tank you took out is not an original tank? and you have to cut a hole to fit another sending unit? Must be a special application you have there. The repro tanks should almost be like original.
From what I can tell this is the original tank,
Yes these tanks and sending units came on SE challengers and Gran Coupes ,
so as you can see the factory had a hole on top for this unit,
and I cant find any tanks with the hole, also my concern is it looks like they just threaded it right in to the steel with no backing plate.
so it did leak,
I am not sure exactly what I will do I have cleaned up the sending unit and it still works and is a pretty rare part,
I just need a plan to do it right or not at all