Put together a 425 from parts of about 5 engines. It runs great and with a 3.08 rear end and a 5,000 pound car it spins one tire with just 1/2 throttle off the line. I am running Tom's pistons and Russ's camshaft. It has quite a vibration at 1200 RPM parked in neutral. I do not feel any vibration when driving. My vibration damper looks good, its from a 1959 401. The flex plate to the turbo 400 is assembled in the index hole on the crankshaft. Anyone have any experience like this? I would assume these engines should run real smooth.