On an A/C car, the blower motor does go in from the firewall side of the heater box. The blower housing with the air recirculation door, comes out seperately from the rest of the heater box. Working through the glove box opening, it can be dropped down under the dash for removal.
The full-size cars (Crown Vic, Marquis) of those years had the AC compressor on the passenger side and the Alternator on the driver's side, but they used two belts if I recall. Brackets might be adaptable though.
There should be some rubber flaps along the each side of the radiator tanks, attached to the core support, "sealing" the air flow from going around the core instead of passing through it. The ones on my 88 had deteriorated and fallen off.