Update time!
Spent some time under the truck today. I have decided to move forward with the assumption that the timing mark issue and the driveability issue are separate. As such, I decided to try timing the engine with a vacuum gauge. This, I thought, went well. I discovered the engine ran better, with more vacuum at idle, with the port where I had the PCV valve plug in, plugged. I moved the PCV to share a vacuum port in the manifold itself. With the vacuum advance port plugged, I was able to get about 18 in Hg. With the vacuum advance attached, I managed about 20 in Hg...steady. The idle seems a little high, but I can adjust that down later.
With good vacuum and smooth idle I was excited to test drive the truck. Made it an entire city block before I hit the gas and it fell on its face. Still, any load on that engine and it isn't happy.
Talking to somebody at NAPA, he suggested going back to basics, plugs, wires, spark, gas, etc. Clearly it's getting some spark and some fuel. It makes noise, vacuum, and idles. Heck, it is sorta driveable. But clearly the quality of the fuel delivery or the quality of the spark is impaired. I tried putting the cap from the old distributor on, that did help a bit. I found, finally, the old rotor and will try that later as well. (By old I mean I replaced them when I bought the truck and they've got a few hours of testing on them and maybe 100 miles).
I'm also thinking I should test the spark plug wires. I'll check their resistance and make sure they're all up to snuff. I have checked the spark plug and that was fine.
Engine compression? Would a bad cylinder do this?