1988 C1500 HVAC install help/guidance

[Grandpa’sTruck]

Hi, I’m new here. I recently acquired a Chevy C1500 1988 4.3L v6 Cheyenne stepside from my grandfather. The owner before my grandfather had an after market AC system installed on a stock HEATER ONLY truck. So on the truck it has the manual cable slider switches for the vents with the knob for the blower motor. Doing this the owner had disconnected the stock heater connectors from the blower motor and had two connectors wired in to use the AC system. Preferably, I would like to be able to use the heater when I need it, rather than having to unscrew the glove box and disconnecting the AC. So i was wondering if Its possible to pull a HVAC system from a 1989 C1500 HVAC system or will I have to find an 1988 C1500 that comes stock with a HVAC system and install onto my truck. I know the stock HVAC system uses servos to open and close the vents so I’m looking for any guidance or help.