By 1975, there were no performance parts on those 454 motors. I just picked one up for my Chevelle, it has a fresh rebuild in it, but its a daily driver. 8.25-1 compression with the small port truck heads. The guy did however put in an Rv type cam and a double roller timing chain. i added a wiend Stealth dual plane intake a set of headers and a 750 vac holley. See what i get out of it. as long as i have passing power on the highway i will be happy.