Seems like the problem bounced around a bit, but in the old thread ph23vo mentions you might have the big rod.
If your engine has the "six pack rods" which were much bigger than the LY rods you need to have a specific harmonic balancer, AS WELL as a specific flywheel. Even though it is a steel crank. With the six pack rods there isn't enough weight on the counter balance weights of the crank to offset the weight of the rods.


If you DO have the six pack rods, then AFTER you get the proper balancer (it will look assymetrical, with more weight on one side)you then need to have the whole rotating assembly (pistons, rods, crank, balancer, and flywheel) ALL BALANCED TOGETHER.

IF you DON'T have six pack rods, then you need to get a harmonic dampner and flyhweel that are completely symmetrical (no weights on one side)
and it should still be balanced, although this time balanced without the dampner and flywheel.