Dave,
What kind of pully width did you have? The 57 motor seems to have a narrower (3/8th ???) belt. The balancer I am looking at is at the damper dudes. He can put the double pully on a balancer for a 292 chevy. I believe it will be about $125. I figure that If I have to buy a new damper, I should get one that I can use for air-conditioning. Did you add power steering as well?