Help with diagnosis??

[CCCC]

1972 Longhorn, BB 402 with 4 speed manual. Almost ready to take this long-delayed project to the paint guy - realized that the truck had not been on the highway for a while - so went out to test.

Ran fine at low speed on 3 miles of gravel, hit the pavement and ran it up to 60mph. After a mile or so, it slowly lost power/revs and eventually would not even idle. Normal temp and oil pressure before it died - no odd noises. Good fuel delivery to carb (filter OK) and would start but not gain any revs - stalls when asking for revs/power under load. Towed it home.

First thoughts and efforts:
Fiber cam drive gear wear and off timing?: Removed timing gear/chain cover - still fiber gear in there and some slack in chain - will replace all. But - timing match up not off enough to cause such a problem.

Has stock dist, so maybe PO defeated the resistor wire that decreases running voltage to ign points and maybe they are fried. Will remove dist check this next, as well as bad dist cap, etc.

Problem with dist drive - at drive end or in dist shaft? Will check this too.

Bad coil function? Do these old coils die slowly, or suddenly?

Other estimates from you folks? Thanks for any ideas.