As for the two or three grove harmonic balancer, I used the two groove style that was original to my engine. I added a pulley to the front of the balancer that bolts to the hub of the balancer just like Chevy does on V8's. Two advantages with this. I didn't have to go find a three groove and the extra pulley retains the balancer outer ring in the event of failure. I had one harmonic ring fly off, while I was driving down the freeway. I had another fall off on the ground, when I started the engine. The next one that fails may screw up the gear cover, but it's staying on the truck.
