Haven’t looked at a wiring diagram, but what you describe is common misswire in 55-57 chevys at the ignition switch, or a bad ceramic dropping resistor mounted on the firewall. I’m guessing you have an HEI distributor. My wager is on it or its wiring.
Many years ago I dug in & learned the zen of just how Quadrajets work and their common issues. I never considered jobbing out something that you could learn & do yourself. No dealing with getting screwed. No question about what was done & good insight to any remaining issue. It’s called a man...
Pulled & parked the plow off the K20. Officially called the season. Impressed w/ the way Rustoleum Massey Ferguson grey held up for the winter. Filled the temporary tank w/ 90 octane non ethanol & she seems to like it.