Powerslide transmission...whats it from/worth?

[NeinH20]

Ok, I KNOW it's called a powerglide, not slide..but every PG I've ever come in contact ends up being a power SLIDE not long after I meet it.

This is an aluminum case PG, that as far as I can tell so far, just has POWERGLIDE on the side. It's very old, but was rebuilt 4 years ago, put into a 55 chevy, and run for 3k miles behind a 406SBC then pulled when the car was sold. I bought it, with plans of putting it in the 63 Impala I had, but opted for a TH350 .

Where will I find casting numbers and what not to find out what this trans came from originally? Also, what would this thing be worth? It was rebuilt while in the hands of a very close friend of the family, but I have no proof that it was ever rebuilt. Any info would be oh so very helpful! Thanks guys.