The mains need turned down to 400 size and the counterweights need turned down to 7.25 ish diameter. Then you can run a 6.76 rod and a 1.32 ch piston which is a popular piston for many combos. I'm doing a 3.9 offset stroke with a chevy 6.70 rod and 1.32 piston. It seems people are always very happy with the 451 combo.