[jonnyk]

I agree with the above except for the blanket statement that a "331" will not fit in a stock block without clearancing. Mine does. It depends on the rods mostly, my Scat I beams fit fine but I know the Eagle H beams need clearancing. That would be something to check on with your machinist once you get going.
I also have an aluminum flywheel on the street and the manners are perfect...the bigger motor doesn't seem to notice the change in inertia, and it freewheels nice on the bigend.