By way of introduction, I'll just mention that I'm an engineer and a mechanic and I'm in Australia.
I don't know if your system is the same as mine. Mine's a 1977 392 with AT-540 and the governor is purely vacuum operated.
I disassembled the Holley from my 392 today, with the intention of adapting an OHG brand LPG (propane) mixer onto the throttlebody, and re-mounting the governor onto it.
After looking at how it works, it appears to me that the system is as follows:
The control for the governor is a centrifugal device in the distributor below the ignition section. It is effectively a vacuum on-off switch that turns on its output at governor RPM.
A vacuum hose goes from the middle of the left (as in left when facing forwards in the bus) side of the carb forward to the distributor to supply vacuum.
A vacuum output hose comes from the distributor back to the vacuum diaphrams on the carby that actually close the throttle, with a bleed back into the carb.
After pulling it apart, I'm pretty convinced that if you blocked either vacuum hose and changed nothing else, you'd completely disable the governor and everything else would still work.
I'm also pretty certain that there is a ring clamped around the governor section of the distributor that sets the governor speed. I'm not sure yet but I think that if it was loosened and rotated around the distributor and re-tightened, it would alter the governor setting. I haven't cleaned it to see if there are any markings on it.
I intend to chase up info on this from my local International/Iveco dealership. I think they'll help me as I do work for them.
I actually came here looking for info on what the correct governor speed is supposed to be. I thought that the governor was supposed to be set to something like 3200 to 3500RPM on an auto because the AT-540 and similar model gearboxes didn't like any more revs than that, but I was looking at an owners manual tonight that quotes HP at 4000RPM!
If it turns out that the governor isn't needed to protect the gearbox from over-revving, I won't bother refitting it.