full Chassis busses sometimes had a dash air option. the IH 3800 did not.. the late model IC busses have a Dash air option.. the freightliner C2 busses offer it as well since those have essentially an FL box truck dashboard (complete with vents even in non AC models)
I used ProAir LLC equipment in my build in which I completely Gutted my driver heater / defrost box and rebuilt it with a Frigiking heat / cool unit to provide driver heat and Dash A/C up front.. its 20,000 BTU.. the unit gets Ice cold but on a hot day running it by itself results in little more than cold air blowing on my body.. the bus is definitely not cool.. it did better after I Dynamatted and rebuilt my floor where the chassis / body join and stopped off most of the heat from under the hood.. huge help..
I did go ahead and install a Mid ship 40k BTU system (rated at 50 but I adjusted the TxV a bit to balance front and mid unuts) and piggyback it off of the same compressor as the front.. Sanden SD7 Enhanced compressors have amazing abilities to move refrigerant.. (no knockoffs no china BS but only the real thing).. I run an ACT (proair) CS3 skirt mounted condenser with 3 SPAL fans to move the heat off.
and finally i added a 45k unit in the rear of the bus its a repurposed Carrier EM1 with a ProAir 3 fan condenser I had laying around, and a 2nd Sanden SD7 enhanced (I always keep a couple of those new in the box ready to go)..
Now its meat locker time baby!! the temp display on my driver unit was 68 the other day driving into the sun 330 PM.. 93 outside with dewpoint of 72.. my sunglasses fogged up immediately on exit of the bus when i parked..
now thats a 31 year old bus with only stock insulation.. High headroom with Tall non tinted windows.. probably the hardest thing to cool out there.. 7 window bus..
my little 6 window red bus.. it has a Trans/AIR from the factory rated at 50k BTU.. its got heavier factory insulation, low headroom, tinted windows.. and I stay sort of O--K-- in that bus on those real hot days, takes forever if the bus has sat in the sun all day.. so i'll be adding a small front system to it
bracketing up a compressor to a 444E is not the same as a ford 7.3, the belt system is different.. you need to either obtain a bracket set from a bus junkyard or purchase an aftermarket set.. from soneone like APair or bracketry systems, maybe red-dot. CHeapest is finding a 444E bus with A/C and robbing it for parts..
NEVER use a ford 7.3 A/C compressor.. those FS10 compressors ford used are royal POS's!!! ive cleaned up more than one ford after "black death".. seemed to happen in the vans with front / rear systems the most.. sometimes the older explorers too.. those were nippondenso compressors..