well... i'm not sure in the differences in the block design.. but i know that a 4.2 crank has a longer nub on the end of it where the balancer goes... for the stroker, i know this nub has to be cut off, or compensated for... there MIGHT be some mods that need to be done before just putting the 4.0 balancer on.. but the block might be thicker there, or there may be another accessory there to compensate on the 4.2 block