I would think that though parts may be a bit hard to find depending on what you are looking for - that the ZR-1 would be easier to find stuff for then a '75 Porsche...
As to the seats - I am 6'1" 230 and have a 90 with the tight Sport seats. Hate em. But I have a set of 95 Sport seats in the garage right now, and the wiring harness and lumbar pump for them are in transit - So the seat problem is fixable...