need some help for a newbie.

The balancer you describe sounds like one made for a cast crank 340 (72-73 only) or a 360...if memory serves, the cast 340 balancers actually have For Cast Crank Only cast into them, 360's just have the cast counterweight.
I can't say about bb stuff...
Can somebody come up with some casting numbers to help this guy find out what he's dealing with? Could be a motor assembled out of spare parts....not uncommon after all this time.
The block will have the foundry casting date on one side of the block, and the vin on a pad under the cylinder head deck on the driver side of the engine.
Hope this helps some...
Alan