I think the AC plugs for that engine with a normal ignition system was an R45. These plugs are the same plugs that were in my old 68 Chevelle with a 307 which had a 9-1 compression ratio so they should do OK in the 235. If you plan to run at full throttle a lot you may wnat to go to a colder plug but you would have to be pulling alot or running really hard to damage the plugs or bet preignition. You said you shaved the heads but you didn't say if you did it to increase comp ratio or just true them up. If your at 8.5-1 comp ratio or less you'll probably be OK. I don't know if these old plugs will stand up to the higher voltages of HEI or not but your local speed shop should be able to help you there The bigest problem with taking an old engine to HEI is the original style spark plugs are set up to have the gap set at about .030 inches and are manufactured so that the ground bar on the tip parallell with the flat portion of the electrode tip. HEI gaps are usually .045 to .060 which gives a much higher voltage and higher energy spark but an old plug set at this gap will not be parallel with the electrode so it won't work as well. A speed shop could probably help you wit this especially if you can find one that has an old timer at the counter that used to run the old Chevey's. Remember chevy had a 302 in the Z28 Camaro that was rated at 290HP at about 3200 RPM (because if it was rated at 300 + HP the insurance would be outragious) with a redline of 7500RPM. The true HP from factory I heard was somewher over 400HP and this was with a points type distributor. Of course that was when they had Ethyl fuel and a 12.5 - 1 comp ratio.

Kenneth L. Hollingsworth