I'm doing an 83 Malibu wagon. Plan to have it running in June.
On the GN harness I cut off the C100 bulkhead connector and spliced in the 83 Malibu C100 connector (hopefully your elco still has it's C100 connector so you can splice it in). The circuits that the Malibu did not support are covered by a small racetronix fuse box I added under the hood. Fuel Pump / Inj, fan relay, ignition module (CCCI), and ECM solenoid are covered by the new fuse box. Power to the fuse box comes from the Malibu's pink distributor power feed (key switched). Conveniently enough, 3 of those 4 wires are pink w/blk. Only the fan relay feed is brown. So now when the Malibu is keyed on, that pink distributor wire will power up those GN items.
Since the grey fuel pump wire does not exist in the Malibu, I gave it a single cavity weather pack connector where it would've entered the C100 and will instead add a grey wire into the loom of the fuel pump hotwire kit to trigger the large fuel pump relay in the rear of the car.
I haven't done the 437 connector yet over by the glove box but I know there's one or two power feeds there and maybe a ground or two to worry about.
Also looks like the HVAC connector is the same 4 cavity between the two cars. Only difference is my Malibu has a 3 wire pressure switch on the A/C and the Buick has a 2 wire so I have to sort that out too.