Just a bit of an update.
My rough running problems have tentatively been solved with the discovery of a broken spring in my fuel overflow valve, on the back of the IP. Thread here:
617 weird behavior diagnoses
I pulled the rear angle iron "bumper" off and bolted on a trailer hitch. The hitch was originally meant to hang below a stock bumper, which put it WAY lower than I wanted. Out came the reciprocating saw and the welder. I was busy, didn't get before or during photos, but got a couple as it sits now. Beveled the edges of the cuts and made several welding passes on each side for full penetration. Some cleanup needed on the back of hitch, mostly removing excess material. The welds won't win any beauty contests, but they ain't coming off either. I'll clean up the whole thing and paint it this weekend. Also moved the backup light and it's fatigue-cracked mount up to the bed, and fabbed my own mount. Like most of my work, it's solid, functional, and lacking beauty.
I added side marker lights to the front of the flat bed, and LED license plate lights below the side marker, tied in with the backup lights. These illuminate the area beside the truck and make backing up in tight quarters at night much nicer.
The timing device has a good bit of longitudinal play in it despite a new intermediate shaft bushing that restored play to spec ~10k miles ago. Something in that area is knocking pretty good too. No choice, going to have to tear into it again, and sooner rather than later.
Think that's about it.
Pic 1 new hitch
Pic 2 new side marker light and side backup light
3 and 4 my ugly welding