Driveshaft question

I ordered a new rear end and am ordering a new driveshaft, and I’m trying to figure out the correct one to order
I get it and I understand, my comment about measure twice and cut once was not a literal cut, it was a metaphor.

But untill everything is in you will not know if it is the correct length, and may end up buying another shaft.

The parts book SHOULD have the correct length for a particular combination of car, trans, and rear ASSUMING it ever came that way. But mistakes are made in parts books.