“That being said, I’ve got no clue where to start.”
Yeah Icee I don’t have much clue yet either.
Your pics don’t show the rest of the truck. Is the body, interior, etc. good?
Are you intending on saving/restoring this? Do you have legal title?
is it possible you might be better off starting with another truck and using/selling this one off for parts? Given that some parts are gone and most of what you do have probably requires careful resurrection to make workable.....

You are apparently a capable mechanic if you just took out & rebuilt the trans. But it’s hard to offer any help without knowing s lot more about what you are working with.

Best of luck ~~ charger_ john.