Hi jaycoop. I have a little experience with the centrifugal/vacuum governors. My '57 2 ton has the 283 V8 with the stock Rochester 2G 2 bbl., it is built specifically for the vacuum governor application. You are correct with the operation of the throttle, the throttle shaft is not directly connected to the peddle linkage, the governor spring opens the throttle butterflies as the peddle is depressed, if there is a high vacuum it will allow full throttle, if the vacuum is low it will only allow the spring to pull the butterflies open part throttle due to the governor diaphragm opposing it. GM used 4 bbl. Holleys with that same style governor on the 366/427 truck engines into the early 1980's. If you find that your carburetor is beyond repair, you may be able to find one in a junk yard with medium duty trucks. If you want to delete the governor, I would think a normal Holley would bolt right up. The shop manual for my truck spec's the governed RPM at 4000, I don't know about the big GMC engine but I would think it to be close to that. I have a Holley 2300 2 bbl. 500 CFM in the barn, I can measure the bolt pattern for you.
