Pros and Cons to both...
Newer style chassis with more available parts.
Roof replacement is relatively straightforward if you can find a good donor.
You can drive the 280 now and it has all the original parts including harness etc.
You have a more modern FI system with a better electric pump etc
You have ugly 5mph bumpers that will need to be replaced!
You have to deal with a roof replacement
More classic look to the interior and bumpers.
Rarer car (if that's what you desire)
Can be made to look like a 240 a lot easier
It has someone else's V8 swap... who knows how well it was done or how bad the frame has been affected
Wiring harness has been cut up
Water damage. more rust, more work
Very hard to find some unique 260Z parts
Is the least desirable S30 chassis for most people (next to the 2+2 of either!)
My two cents is go for the 280 and restore it the way you want. Drive it for a while for fun and enjoy those memories while it is in the shop for the next year! or three....