Rob,
Busses have the aerodynamic profile of a brick wall, you don't need brakes. It'll slow down naturally.
The 924s brakes are easy. For the front, you can use those hubs with some bearing spacers to fit onto your bus spindle. You'll have to fabricate some caliper brackets.
The rear will bolt on it you get an IRS kit from some of the vendors. The only issue will be the ebrake cable.
The Brembo's require the thicker rotors, and will not work with the thinner rotors.
You didn't mention what year bus.
Lanner