Slant 225 motor codes from VIN and trans mating questions

What I have now is the 1980 slant A727. So if a motor came out of 4-speed manual, I should already have what I need. Seems there's always a catch somewhere, so just asking.
I want to keep my truck in running condition while I futz with a spare motor. By the time I find a Super six setup and all the trimmings, I think I'd rather get a yard motor and build it up and drop it in later. I'm looking at freight prices to make or break that decision.