Harmonic Balancer

[chickenwing]

Last month I finished up my LM1 crate install. I decided I wanted a "Quality" harmonic balancer. Figured anything to increase the longevity of my investment.
Went to the local "speed shop". Asked for a harmonic balancer for an externaly balanced 350. Kid looks up in his book, comes back with a Performance Products balancer marked SBC350. Got home read all the literature (weird that way) discovered it was for an internaly balanced motor.
Took it back. Got the same kid, insisted that was it. Showed him the literature. Says ok. Looks up in book, comes back with balancer marked SBC 400. I said wait a sec, you sure? He say look for yourself, it's gotta interchange. I looked. No referance to an externally balanced 350 motor. In a moment of weakness thought he must be right. Got home read the literature, saw no red flags, and installed it. Me, not being an engine guy, had no clue.
Started up first bump.. Was so proud. Got initial timing done carb halfway tuned... Ran it 2 grand 20 minutes. Everything fine.
Went to take it in her first voyage. Thing started vibratin like crazy inside of 10 feet. I immediatly shut down. checked torque converter by disconnnecting (prior problem) it still did it. Suspect was front side. Posted my suspicions on board had an answer QUICK. Said screw it went to Autozone bought another balancer. Problem solved. I still wonder if crank bearing surfaces were prematurely worn cause of my ignorance.