Chevrolet: 350 rebuilt, motor wobbles, oil leaks, main bearings

Question
I bought a 74 Nova for my son and the engine has been replace with a rebuilt 350 from the mid 80's.  When the engine is idling there seems to be a wobble that can be seen on the front pulley.  We replaced all the pulleys and still wobbles.  If you increase the rpms the wobble goes away.  If the original flexplate (1974) was used and the mid 80's damper used could this cause the wobbling?  Are they different weights from early 70's to the mid 80's.  The engine seems to run good, no noises or oil leaks, oil burning.  Should we be concerned about anything else?  Thank you for your time.  Ken

Answer
Ken,
    Using the flexplate and harmonic balancer combo you have shouldn't cause that, but if the balancer is bad, it might. The first thing I would probably try is a new or different balancer. If there is no noise from the motor and no leaks, I probably wouldn't be worried about the crank being out of balance, as the first thing that would probably happen is an oil leak from one of the mains. You might check your flex plate to see if a weight has fallen off, but that is an outside shot at best. The main thing to be concerned about with any kind of wobble in the crank area is the main bearings and seals. Try a different balancer, and let me know how you make out. If it doesn't fix it, I'll dig a little deeper.