Re: What is it?
could be a TH350 700R4 or possibly a 400. If you have overdrive it's a 700R4. Anyway crawl under the truck look at the tranny pan, if it's square (or close to) you have a 700R4, if it vaguley like texas it's a 400, if it is a square with a corner chopped off 350. You can also look for the modulator, no modulator 700R4, modulator comes off towards the back 350, off to the side it's a 400.
Engine block stamps, there is normally one on the front somewhere not really sure where never looked. Sometimes crate engines have a tag like that on the transfer case on the drivers side of the engine.