FWIW, I run my '59, w/ 64k miles, and use unleaded premium, 91 Octane here in L.A. The car is completely original, I don't think the engine's ever been apart. No knocks, seems to run fine, and I've had her at 90mph for short bursts here and there. Every now and again, I'll put in a little lead additive... I might use more if I ran it for extended runs, but I rarely put on over 100 miles at any one time. If I ever do the head, I 'd probably have the upgraded valves put in then. Of course, YMMV!