Long time, no update!
It only made it halfway home from picking up the 1991 drivetrain. The transmission died hard, and not in a Bruce Willis action movie way but with a loud squeal and failure to proceed. So it came home on the back of a bigger flatbed and the swap process commenced.
The 1991 engine got mostly taken apart. New King crank and rod bearings. New billet aluminum distributor to replace the original that had near 1/4" of slop in its shaft (HOW did the thing even run at all?!?). New piston rings and honed the cylinders. Also put in a new oil pump and timing set along with all new seals and gaskets and a thorough de-crudding of the oily, explody and wet areas.
I sold the 700R4 that came with the 91 engine and bought a rebuilt one online, with the mechanical speedo drive parts added. Speed signal to the ECM is provided by a 2 PPR adapter from Jags That Run. It also got treated to a new TPR and pair of injectors and a new O2 sensor. Bought a threaded bung, drilled a hole at the Y in the 1982 left exhaust manifold and brazed it in.
The cheapo idiot light cluster with nothing but a big fuel gauge and speedo got swapped for the version with proper amp, temp and oil gauges. Same connectors but had to relocate a lot of wires in them.
After wasting tons of time trying to figure out why the stock 1991 electrics would not open the injectors and squirt fuel, I spent $375 for an aftermarket wiring harness and GM ECM with modified programming that's supposed to lock up the TCC in both 3rd and 4th. It also did away with the ESC module and knock sensor. How? I don't know, but it runs really nice.
Much progress has been made putting it back together, got the front back together, got the new dash pad installed too. Picked an Alpine digital tune two shaft radio from a junkyard - just happens to be the exact model that was OE in late 1980's Lamborghini Countach.
Had to do some creative mounting to fit a pair of 4 inch two way speakers into the stock outboard dash mounts (another junkyard pick) so the tweeters didn't stick up above the stock speaker height.
Had to install a new headlight switch. Original had some internal short which turned the headlights on at the first stop and made the dimmer not work. I also installed a headlight relay kit and new halogen bulbs.
Another mod is a 1987+ tilt column and intermittent wiper module. There's cruise control switches on the signal/wiper stalk but that's an upgrade for later. Of course I had to find a GMC sport wheel horn button to replace the Chevy one. (The Dodge mudflaps are staying, just because.)
Not being a smoker, I came up with another use for the flip out ashtray. I designed and 3D printed a plate to hold three 12V sockets and a pair of USB charging ports. I even put a little GMC logo on it.
Passenger door window is jammed up, won't roll down, so that's on the To-Fix list, which will entail installing the new window felt and rubber kit.
It will soon be ready to roll out... to the tire shop to pay through the nose for having six 16" tires mounted and balanced. I found a pair for the front and four for the back good tires on Craigslist, though one of the four is different. Quiet looking highway tread instead of the rough and noisy all terrain (and leaky retreads on the back) that came on it. Noise = wasted energy = not helping efficiency, right?