I used a Isky E4 cam in mine. It is a little bit bigger than the stock HP273 cam and is a solid lifter cam like the original. I also used the Egge L2222 hi compression pistons. Although they are advertised at 10.5/1 with a valve job, possibly new valves and thicker head gaskets you will end up with somewhere around 9.5/1 The 273 heads are very efficient. And just to correct a previous post, all 64-67 273's had solid lifter cams and adjustable rockers. Please get us the casting number off the heads. The engine build relies on which heads you use. 2 barrel and 4 barrel 273's had closed chamber heads until 1968. We need those casting numbers.