thats most definitely possible.. you need to fimd the condensor for a regular cargo van of the same type. that you can mount in front of. the grille. the limes are usually screwed together with fittings so the fsactory dash air can be connected up to a factory hose set (again for a cargo van of the same model and engine).. then the rear system and the underbody condensors can come totally out.. and youll have the front dash air to use for on the road.. the units in those vans work really well when set up right...
can you drive the bus without it? I would unplug the wire from the compressor as the compressor will operate anytime you turn your defrost on.. and you dont want it to come on at all.. the only trouble you can get in is if it is making noise from the bearings when it is off, it means the outer pulley bearing is dying and that could cause you issues.. but generally if thats quiet you can drive with it unplugged as much as you want.
sounds like the compressor locked up.. so was your unit in back not blowing cold but the dash air was? was the unit in back blowing warm air or none? now neither work? im trying to establish if this bus has 1 compressor running both dash and rear A/C or if it has 2 compressors under the hood.. if it has 2 separate systems.. 2 compressors, a condensor in front of the radiator and the dash system which is completely isolated from the carrier.. then it shpould be as simple as replace the front compressor, flush the system out because of the metal (ford compressors are notorious for this failure).. and then youd have your dash A/C back..
the other type is called a 'Tie-in' system where there is 1 compressor, a condensor under the body (and not one in front of the rad / intercooler).. and then the dash unit and rear unit.. this type tougher to fix because like the shop says, metal could go through everything. all of it needs flushed. im nowhere near california or I could fix it