I would try the 93 ethanol-free and see if it works. You could always cut it with some higher octane stuff. Couple of gallons to a tankful until you find the sweet spot. Ask your father if he remembers during the rebuild if they installed hardened seats when the did the valve job. Chances are you don't need lead substitute. I don't know but my guess is octane boost that you buy is probably just snake oil and probably won't help much unless you use a couple of gallons per tank.