trans swap / interchange in 88 Chev diesel

Hi all. I'm fairly conversant with mopar stuff, but completely
ignorant about GM so please forgive me.

My father has a '88 Chev p/u with a 6.2L diesel and the 4 speed auto
trans went south on him. My questions:

-Is this a TH700R4 trans?
-When searching for another trans, what are my interchange options?
-Will a 700 from a gas engine work? What about a 350 or 400?
-He has an old 3 speed standard (floor shift) that is in a mid '70's 1
ton. Will that work?

thanks
jr