engine specs

Any oversize that your block needs can be used. But to use factory heads, you'll need to stay with a flat top w/4" stroke design. If you went with Magnum or aftermarket heads with closed chambers, then a dished piston can be used. If I recall correctly, the factory spec for a "915" or J/X head is 68-72cc, but the ones I've seen and measured are 72-76ccs. Welcome to factory truth as opposed to specifications. Excellent package by the way (408ci). Ross has off the shelf numbers for this combo.