Rough idle, carb dying?

[68ChevC10]

Argh!

I have a straight 6 250 with a rochester monojet single-barrel carb. Lately the truck's been running *real* rough. When it starts, it's kinda rough the first time I put it in gear. (3-spd auto transmission) As I'm driving, each time I come to a stop sign, I have to take it out of gear because it "throbs." The idle's rougher and rougher. I've heard smoother idling Harley's. Heck, my weed eater's got a smoother idle. When I put it back in gear to go after the light changes, it pauses for a sec like it's gonna die and then catches and I go again.

I've:

replaced the vacuum hose going to the advance on my distributor.
adjusted the idle and mixture screws on the carb.
replaced the sparkplugs.
checked the distributor cap and points.
adjusted the advance on the distributor.
replaced the fuel filters. (I got one between the tank and pump and one between the pump and carb. The tank's original.)

Once the truck starts idling rough, after a while it will do so even when it's not in gear. When it does this, I can pull on the advance by hand and it smooths out for a little bit. Am I looking at a new advance? I don't know how old the distributor is, but I replaced the cap, points and the small coil (not sure of the right name for it) 4 months ago during an engine rebuild. Replacing the advance sounds good, but I don't know if it's the only thing wrong. I've had more than one person look at the single-barrel carb and get that blank look on there face that says, "What is that thing and why are you using it?" The guy who helped me with the rebuild thinks my carb float level is too high and a rebuild is needed or a slight pounding on the carb in the right spot. I'm not one taken to beating on engine parts with a hammer, so that makes me uncomfortable, but a carb rebuild does too.

Any thoughts? Tempted to order that 2 barrel carb I've been looking at.

68ChevC10