This problem has found its way to my door on a few occasions. Once, an older Ford with a 2150 2bbl had rust accumulated in a small wire mesh filter which was part of the needle and seat assembly. Another was a 1 bbl Carter bbd which had a power valve hose twisted so as to prevent the float from dropping down far enough to allow fuel to flow above a fast idle. And several cars have had the emulsion tubes partially restricted with gum and shellac from long periods of non use but the Sea Foam should have made a noticeable improvement if that were your problem.
Well for me all my life its been either guitars or jeeps. Not much made its way in except 3 wives, but the last ones a keeper. (BTW, I still have all the guitars and jeeps I ever had)
I play classical and flamenco mostly. Have written some noteworthy songs, one of the best was in the front seat of a 49 Willys PU where Id spent the night overlooking a deserted beach in Sebastian Fla. Had a fight with (you guessed it) a woman, and she tossed me out. All was better the next day but the Willys and guitar did come to the rescue
Ah those were the days!
A guitar can be less troublesome than a woman or a vehicle, huh?
It could be a timing chain problem. Moving the timing around to get it to run is one of the classic signs.