Just remember to do alot of research first, then look for a rust free, western state Z. I know that the 78 280Z with a 5 speed (not a ZX) came with a r200 rearend.
The 280's have a bit of a stronger chassis than the 240's.
I'm using an LS1 conversion from Johns Cars. I am trying to avoid strengthing the frame rails by using a triangulated front strut bar, and a roll bar in the rear. Even though I have a R200 I have decided to put in a R200LSD that I got on ebay a while back. This is a great site. Search and read then come back with questions. That's how I have figured out what I need to do.
Dale