93 air conditioning in 73 truck

I am fixing to pick me up a 73 club cab truck for a new daily driver. Truck is in beautiful shape, but is a heater only model. I have a buddy with a few 89-93 Cummins trucks sitting around that would get me cheap a/c parts. Has anyone ever tried putting the blower box out of a 92 into a 73? Or am I better off trying to find year correct parts?

The firewall holes are different. The 72-80 is shown here.

81-93

I'm putting a 84 firewall in my 77 CrewCab so I can use the later A/C parts that are easier to find & I can put the serpentine system back on the Mag motor & use 92-93 A/C lines & compressor

Looks like for my purposes finding a 73-80 a/c unit would work the best. The truck has fresh motor and paint so I am not looking to tear it all apart. Although I just realized looking at some other pictures that heater only trucks don't have dash vents so I would need to find a dash or put some into the current dash. Maybe I need to see if i can find a used aftermarket under dash setup for cheap, that would probably be easiest.

we put a 92 LE club cab,
cummins fire wall into a 73 crew cab

so that the car hauler ended up with

A/C, tilt/cruise, pdl,pw, and cummins 5-speed , 3.07 gear

was 440/auto, 4.10

Vinny, a member here, 66fastback i think.

Put the entire dash and HVAC system from a 93 into a 78. Worked great, and the updated HVAC is much nicer.

Just make a template out of carboard and trim the older firewall. Take a little at a time and test fit often. Easy swap.

How about the vents and controls, would the dash need to be swapped as well or are the vents adaptable? Since you would have to cut vents into the heater only dash I would think this would work ok, but the controls may be harder to adapt.