I would like to know as well. My LQ4 in my 78 Bu just hit 11.34 @ 119.5 shifting at 7500. 134k short block, ported heads and bigger Comp cam. Hasn't blown apart yet but not sure if it will. But $450 for a balancer hurts.
I think the only problem you would run into with a stock balancer is that they are not designed to dampen harmonics above a certian RPM range. That and you cant be for sure that a factory balancer wont come apart at that RPM range either. JMHO. I am running an ATI dampner on my factory bottom end in anticipation of high RPM harmonics. Aftermarket dampners have better tolerances and better "materials" to dampen harmonics. And once you start dipping into single digit time slips, SFI parts become a concern. Another reason I chose an SFI balancer and flexplate. Again, JMHO, Eric L
Personally I would not do it. Its cheap insurance and piece of mind to get an SFI Balancer. You dont have to spend alot of $ on an ATI although you can go wrong. Powerbond would be the next best and affordable choice. They look trick too!