I went through the engine on my 68 Z a couple of years ago. I went with all stock components except for roller tip rockers on my 302. I typically run about 10 gallons of 93 octane to 5 gallons of 110. Many times however, I run straight 93 with no detonation (total timing set to 36 degrees and running R45s). At first, I couldn't believe I could do this but then I read this
article in Chevy Hi-Perf and it makes perfect sense to me. So those of you running hi compression + long duration cam may want to take this into consideration.