Assuming its a carb setup being the ECM is gone. AC is controled by the car, not the ECM. Only thing ECM did was activate fans and up the idle on the EFI cars. Carb cars have mech fans and an idle solenoid for the ac. Its not hard, you just need the right stuff. To start, I would identify the extent of what you have. The wiring and controls would be where I would start.
Your best bet is contact a third gen dismantler. There are a few on FB. The fellow below has stuff and there is a fellow in PA that has stuff that I can't seem to find his contact at the moment.
https://www.facebook.com/mike.roark.33