I'm one of the origional owner crowd. Purchased mine in July 1970. Drove it home on Dec 7 1970, so 39 years, and 3 days of driving. It now has 260K miles and needs a paint job. Rich Nedinsky San Jose, CA
I had the same problem on a 1970 240z. It would throw a rocker off at startup periodically. My problem was loose valve seats. Took the head off. Three of the valve seats were so loose the they fell out of the head when the valve was opened. When the engine heated up the aluminum head would expand and lock the loose seats. The Fix is expensive ... New seats for all the valves.