Turns out its a a '74 (not '73) SS 454. The current owner tells me he has '66 heads on the stock '74 lower end. Says he has to run a mix of racing fuel and premium to keep detonation down due to the 10.5:1 compression...

Is this what you were refering to?

Don't know if I'm real fond of having to run that mix of gas. I was looking for pump gas friendly daily driver mods...

Thanks,
Sean