Where to start

before you rebuild the engine again, i'd like to know more info about the carb.

the bottom end generally dont make the engine run wrong unless he got the timing gears way out of whack but that's pretty hard considering they have little arrows to line them up. even with the 4% manufacturing variance or whatever it is, that wont make the engine run bad. possibly if you used the old cam i could see issues. was the cam a new stock cam or just the old one?

i'm guessing it was a new stock cam and that he installed the timing gears correctly. not perfectly tuned unless you degree the cam but still, this would not make the engine run real bad, it would just be missing a few horsepower that you could get back by optimizing the cam timing

that being said you more than likely have a distributor problem or carb problem.

out of those two i would lean toward the it being carb problem.

the reasons are #1 you probably have an old gas tank with crap in it. #2 the carb is probably not new. #3 if a carb is old or not rebuilt right the truck wont run right. heck even a lawnmower with a bad carb wont run right, and those are a whole lot simpler than automotive carbs.

just my 2 cents