My 70 LS5 has a 75 454 and turbo 400 in it now. I have a correct casting number and date coded motor for it that will be my winter project. Is the 75 trans the same as an original 70 turbo 400, other than the date tag? If so, I will probably rebuild the trans and just remove the tag. Any suggestions? Thanks.

Unless you've decked the block or had the engine id code removed ,why bother as it'll never be 'as born' again unless you find the original engine.
It's easier to see the engine id than the trans tag.

The block has already been decked when it was rebuilt. I'm not so worried about that as being curios as to whether the transmissions are physically the same. It's a real LS5 car (build sheet), I am just partial to cars that appear original down to the last nut/bolt. I hope to never sell the thing, we've been through too much together.

Yes ,physically the same ,some internals are different but shouldn't matter.

both the original and your replacement should have the short output housing

Thanks for the help.