To be honest, chamber size really won't do anything towards what plugs needed. Most SBC's from the early '70's ran AC R45TS plugs. Biggest thing would be if you would need a hotter or cooler heat range plug which would be the likes of the AC R43TS, R44TS, R45TS or R46TS. I personally run R45TS or its equivalent. Biggest thing would be would basic, platinum or what every long life plug would be best suited for you needs.