I have had excellent results with Bardhal Instead O Lead if you can still get it. Like over 100,000 Miles on an 67 truck 283 310K miles total with no valve failure. If you need octane (50k miles On Buick 350 you can use the Instead of Lead Gold if theyse still exist.
I will second this, it was the only lead substitute available in the US that passed a series of tests that the Federation of Historic British Vehicle Clubs performed a while back. Not that they are necessarily the be all end all, but their comprehensive efforts are the best tests on lead substitutes that I have seen. Google them if interested.
That being said, I have taken to using a mix of 100LL and 94UL aviation fuel on our antique boat. This solves two problems; valve protection and ethanol issues as they are 'pure gas'. They are also very stable fuels, believe they have to last 24mos. at minimum. Bit costly, but we don't use the boat that much and it works.