I have a .030 over 400 engine with 670 heads on it, TRW's replacement for stock flat top pistons and 460 lift. It runs very well and very strong, but it would never tolerate 91 octane. If you plan to use pump gas you may want to get larger chambered heads rather than machine the 670s (as they are still sought after and do run well.) As mentioned, if you do use the 670s and plan to use pump gas, get dished pistons. Or, if you don't drive it every day and you don't mind the mixing you can use octane booster. Mine runs exellent and has great throttle response with the high compression. I love it, and have no problems. I also use octane booster for way less $ than the racing fuel. However, I mix it exactly the same each time I fuel so I never have to change the timing.