I have a 78' c-60 that came with a trashed 4-53t detroit (anyone need parts eng). came accross a 427 truck engine (tall deck) with no flywheel. purchased a used flywheel and a dual disc clutch . since none of this was in the truck and I put it all together there is a vibration at I would say 1500 to 2000 rpm then it goes away. motor idles sweet no smoke or vibration. wondered if I got wrong flywheel? this was 7 years ago when I bought all this stuff finally got it all running again the other day. is this motor internally balanced? can't remember. the clutch has a floating plate between the clutch disc. wondered if it could be my problem. going to have to pull trans and see if flywheel is indexed to crank pin. will end up removing clutch and firing up to see if vibration goes away. any thought or experiences may help. don't do like I did and let stuff sit without getting back to it .