you would need everything out a 94-95gt(maybe some of the foxbodies would work too)
It'd be a lot easier if you had a 94-95 Gt. You could just drop a 5.8/351efi and use the 5.0's harness and computer.
I just looked it up it would need 84-95 mustang 5.0 engine mounts.
It would be a huge project and if you have the chance it would be a lot cheaper to pick up a 94-95 GT either as a parts car or try and sell your V6.