I agree 100% with Ross and Jay that a chamber shaped dish is more efficient. I also think that for what you describe, I would still use the Sealed Power piston. That is a lot of difference in C/R, and on the street, you might find yourself running one to two more degrees of timing to light the mix under the quench side. A four valve relief piston is actually better off to have the round dish intersect the quench-side valve reliefs......otherwise you have a couple of valve notches trapped under the quench side with unburned fuel there. Rebco is a very capable outfit, but if you are talking about $179 Hypers versus custom stuff from Rebco, it is a whole different world. I have had stuff done by them that ended up north of $2K for eight pistons. I have CP custom make my stuff, and if I do five sets at a time, it can get reasonable for budget builds, but still not as cheap as shelf Sealed Power stuff. The advantage of modern ring selection, to me, is worth more than the cost difference. The KB and the Sealed Power use antique rings with high tension and huge radial thickness. Depending on what you are doing.....there are advantages to the high silicone hypers in certain situations, like a daily driver, or a mild performance street deal. I would suggest investing in a creative ring package even for the lower cost pistons, with a steel top, cutback Napier 2nd ring, and a gold Hastings oil ring package. We have done several engines with those H304P pistons, with custom rings, and they really do a jam-up job. Just running those numbers, you must have a 68 cc head? None of the factory iron is that small unless you mill them a fair amount, unless you have early heart-shaped 352/390 heads. Point being, a flat top, with two reliefs comes out pretty nice if you dont have chambers that small. I'm sure you have checked them, but most of the heads will be mid-70's or more without an effort to make them smaller.
