I have engine #'s but still can't nail down exact dates. What is this thing!?

[ur2noz]

Just became a new owner to a 1970 C10. Truck has a non-original 350 in it. The engine # is V0525TBB with casting #3970010. It appears from all my research this could be a 1970 255hp 350 but could also be a late 70's 165hp 350. Clearly there is quite a difference. What other info can I look for to really hammer out a positive id? I thought maybe a compression test? Higher compression motor more then likely the high HP? Need some direction here. Also where on the trans will I find identification numbers? Its a 350 3 speed.

Appreciate everyone's help

Adam