Dave - prolly would be nearer the low end [I had a pair of 283 heads done for about 500], but why bother? if it runs well it will continue for many miles, and if symptoms of burned valves/ recessed seats start showing up, then that's the time to spend the money
remember that unleaded has been the norm for years already, and there's still many older engines that haven't shown any effects yet - my 235 had 50,000 on it when I got it, and has about 85,000 now - still hums along and I've always used unleaded
Bill
