1) fabricated and installed a ground strap from cylinder head to frame.The ECM was reporting a 172 O2 SENSOR EXCESSIVE LEAN condition. That was from when the O2 sensor was unplugged.
2) Replaced the plug wires.
3) Took the coil off, cleaned rust from the other coil's mating surface with a wire brush, and cleaned the corresponding surface on the coil bracket, thus insuring a good ground.
4) Installed coil.
5) Read the ECM error codes, then reset the ECM.
I used the coil which was the original piece for that engine. It had rust on its mating surface so I wire-brushed it; and did the same to the bracket. This ensured that the coil's ground connection was as good as it could be.
The Haynes manual claims there's a ground strap from cylinder head to frame. There was no such strap on this car when I removed the original engine. The strap I made is bolted to the coil bracket, which is bolted to the cylinder head; the other end goes to the frame.
The plug wires were the wires which I'd originally installed on the replacement engine when I was rebuilding it.
Once everything was buttoned up, then I tried hooking the vacuum gauge to the manifold; the hose was long enough for me to set it on the dash and there's enough of a gap between hood and cowl that the hose was not pinched shut. Thus equipped, I set out to gather data.
I drove probably a total of 18 miles or so, in a variety of operating regimes, and it quickly became obvious that the stumble was gone.
The odd surging I was getting when in gear and slowing down with throttle closed (high vacuum) is gone. I can drive at 35 MPH in fifth gear and it runs as smooth as you please. Step on the gas and it accelerates smoothly, with no bucking or jerking.
The Great Jalopy Engine Swap Project is now officially finished.
So what did we learn from this project?
1) ALWAYS CHECK YOUR GROUNDS!!!!!!
2) Always replace wear components even if you think they're perfectly fine.
3) Even if you think it's obvious where a hose or wire goes, LABEL IT ANYWAY. And take pictures. A 1 GB SD card costs $15 and stores 600 high-resolution images; there's no excuse for not taking lots of pictures of everything so you know where it goes.
4) Before painting a piece of metal, wipe it down with solvent. A wire wheel won't get the residue off. (The paint on the valve cover is flaking off. DAMN IT.)
5) ALWAYS ALWAYS ALWAYS CHECK YER GODDAMNED GROUNDS!!!!!!!!!!!!!11
Next up: removing the oxidization from the headlights. I saw a nifty tip on one of my car shows; you can use toothpaste and a buffer wheel to do it....