I bought a Hays flywheel from Summit Racing and wished I hadn't. It was lighter and thinner than a stock 400 sbc flywheel. Lighter is bad for 4 wheeling. As for thinner, this caused my brand new Centerforce II clutch disk to eventually rub against the crank bolts(per Centerforce). If you can't find a good used one, they are hard to find, I would try getting a replacement from GM. Maybe some here can get you a part number. My .02