Odd question
 

This shows my lack of knowledge about these cars, but im really interested in them. Do the 70-78 Zs need special gas (leaded)? And if so where to get it or an addative?

In theory, the Z L-series engines had softer need-leaded-gas, usually bronze, valve seats 'til something like late 1976. Anyone who has had a head or valve job has certainly long since built to modern unleaded-gas specs (steel seats). And at this point I don't know any Z drivers who use lead additive, here in the states. If anyone on here has some other input, though, it sure would be interesting to see who's doing what with lead, etc. For octane grade, the manual (for 280's anyway, dunno about the 240s or 260s) says something about using premium, etc., etc. but it seems to have more to do with the historic practice of the premium being cleaner, and less that the compression demanded it. Modern gas has to meet stricter cleanliness standards than it did in the 70's, and as much as it's for environmental considerations, it is far better for the motors, too. Plenty of people run lower octane in their (unmodified) early Z's with the stock usually 8.x compression with no problems. I don't burn much gas, and never know what altitude I'll be at, so I just run the premium from a good brand at a moderately busy station and don't worry about it beyond that. Hope some others post on this, too, as it would be interesting to get a variety of perspectives.
Dave

The lead in early fuel was there to add a softer surface at the seats to reduce wear and tear on the valves. With today's unleaded fuels this wear and tear is accelerated. To what extent could only be measured by the engine, driver. and other sorted iffy's. To lay it to rest you can drive the car until it rots away, gets sold, or needs engine work. If it's the latter then you can give the head the well-deserved attention at that time. Drive it like you stole it!