help me ID this

[chevytruckfan]

OK just got my truck home yesterday and started going through it making sure it is safe to drive. As I was checking everthing I also wrote down all the ID numbers on the engine block I have 44 GM 3970010 what type and year is this engine, and anyway to tell what vehicle it came out of? I looked on both front and back of the heads I could not find the #. Anyone know where to look? Same for the trans but I do know it is a TH350 by the shape of the pan and location of the module. I pulled the rear diff cover off and on the ring gear I have 3817778 11:41 GM 12-71. It is a 12 bolt and with the ratio stamped on it, it is a 3:73 rear, but not sure if it is posi? I did not see any springs in the carrier unit just Ring, pinion, and spider gears. But with one wheel off the ground I would not turn. With both wheels off the ground the opposite would spin in the counter direction?