I agree with John.Hardened seats arent a requirement.How many miles do most of these cars get?Usually not many.Not compared to what was a daily driver getting 100K or better on them.My 516s were done probally 12 years ago no seats installed.Now on my kids 413 they get quite a bit of miles.No problems at all.He does run race gas as I did at times but usually just 93 octane from the pump.Rocky