The thrust bearing has 2 surfaces active in accepting thrust 1 forward and 1 backward.I have seen several Chevy type thrust bearing failures but always failed because of forward force on the crankshaft.Clutch release force usually is the cause but I shared a problem with a working buddy on a Big Block that was caused by main bore misalignment.
Have any of you ever seen thrust bearing failure from thrust to the rear?I have never seen one fail from rear thrust.
Another possible detrimental force from driving on the BALANCER is due to the end force transmitted through the "cranked shaft" in other words the shaft is necessarily crooked like a bent nail and if the installing blows were heavy enough the 4 offset "throws" would spring backward and then return with each blow.A bending not needed in a crankshaft.
On the other hand the factory didn't drill the cranks until the 327's I think and a hell of a lot of balancers got installed somehow in the first 7 years.
I would not hesitate to install one with a hammer in a field situation but if it was in the shop it would get drilled and threaded
