My 83 C20 454 had the bolt holes on the crank pulley shear off twice. After the second replacement I guessed that the harmonic balancer was the problem. The balancer did not shear off with the crank pulley, but it was the cause of the crank pulley working off the bolts.
I used the proper Loctite for the crank pulley and used grade 8 bolts after the new balancer was in place. So far so good.
So, in my experience, it is best not to overlook any problems you might have with the balancer.
Disclaimer: I know almost nothing about auto/truck repairs. The value of the above advice is worth approximately $.02.
