Faaaaaaarrrr easier to find a relatively clean shell and toss in a functioning drivetrain. Or repair/rebuild the existing drivetrain components and L series engine.
But be reasonable. It' sa 35 year old car. So unless you're shelling out $15,000+ you're not likely to find a completely flawless example of a Z. Most have rust in the floorpans, below the battery, rockers, etc. etc.