Since you have both cars, I can't see any reason for abandoning your project. The glow system from the early car should be easy enough to wire into the newer car (1980 is the first year for the glow system and the vacuum control of the otherwise similar transmission).
The transmission control system for the old car is all in the linkage so there is less problem putting it in the new car than vice versa.
Probably the worse problem is the A/C compressor will have to stay York as the mounting holes aren't in the block for the GM R4 compressor used from 80 on. The only problem will be the hoses , which shouldn't be much of a problem.
Basically I would rather have the early tranny, but not the early A/C. The glow system doesn't make much diference.
It's almost plug and play, go for it.
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician