Will share my experience to date:
July of this year I acquired early 1974 260z that had been converted to a 350 SBC engine with a TH350 transmission. The car is a "barn find" was last driven in 1988 when parked for some unknown reason and the owner claims it was running when stored away, yeah right. Upon evaluating the car and researching where to take this project it has become clear that a LSx swap would be a vast improvement over the Gen1 SBC. Have not committed to doing the LSx swap yet but strongly leaning in that direction.
Will get the 350 SBC running and see what I actually have as a starting point. Currently dealing with the fuel system that was full of 31 year old gas, very nasty, and the minor rust issues.