When I had the crank at the machine shop, I had the machinist mill out the hole for a pilot bearing and balanced with the flywheel I ordered. It's a special flywheel from cad500parts.com. The flywheel fits 10 to 12 in gm clutches. I used the BOP to T56 bell housing and it fits up to an 11 in clutch. For the clutch, I forget what exact one I picked. One rated to hold 600 hp if my memory serves, but it's a push style to go with the T56 throw out bearing. Hope this answers your question.
