Sounds to me like what happened to my 327 when the governor failed. You could look down the carb and open the throttle all the way, could even see the blades move, yet the engine would just idle. Back in the '70s, Dad's truck (same year C60 just a flatbed vs a bus) did the same thing and he just bypassed the governor. Then it ran fine. I think I did the same thing, and installed an HEI distributor while I was at it because even back then (early 1990s), SBC HEI distributors were a dime a dozen and it was no thing to bypass the resistor wire. Then I swapped in a Cadillac V8, however if my bus had come with the 348 or 409, I would have rebuilt that instead.
