Sounds like you have an intake manifold heater...pretty common on older motors supposedly improves idle and fuel consumption...I installed one on a '58 235 at the recommendation of Stovebolt Engine Co...I really never noticed a difference.
I also have a GM Crate 350 w/ a 600 Holley...won't let me pass a gas station without saying hello! Plus it tends to load up on idle...I've done a lot research on the GM Crate /Holley issue and it seems the major problems involve that carb...moste guys have replaced them for street use...just bought an Edelbrock 600 as well...good luck

Steve G.
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1942 Chevrolet 1/2-Ton Pickup Truck