Man, you struck gold. Underneath all that dirt and dust is a real gem. Just hosing it off will make a world of difference, and it looks like it is pretty solid.
For starters, you can sell that engine and trans to someone fixing up a Chevy of that year, who wants matching numbers. Or sell it to a rat rodder, they love these old engines. (but don't wash off the dirt, they call it "patina." :LOL: :LOL: :LOL: :LOL: )
Not sure how deep you want to get into the build, or your capabilities, but you could either lift the body off and clean up and refit the frame and suspension, or simply clean up everything with the body intact. Frame off would be best, but it takes some work and lots of room to do it. Take pictures of every aspect of the car before you tear it down, and as you are tearing it down, for reference.
I envy you, this is a really historic piece and well worth doing. Gotta get ready for work, so have to run. If you have any more questions or more pix as you proceed, just post them.
Don