As I understand it, hardened valve seats also allow the possibility of burning today's 10% Ethanol gas, and its higher burn temp.
Of course, there's no reason you'd ever want to use such gas in one of these cars unless you had religiously replaced every gasket, seal, hose and bit of rubber involved in the fuel delivery/combustion system as well...unless you want problems down the road as ethanol will degrade everything in its path, not to mention giving you poorer gas mileage...
Just say no to ethanol and yes to the non-lead, lead replacement additive, and screw the hardened seats...ya don't need 'em.
I believer there is a phone app available to locate stations that still offer non-ethanol gas. For my part, I plan to keep a spare 5-10 gallons stored in the trunk, depending on my travels...so I know I can get to the next non-ethanol fill up in areas where they are fewer and far betweener.