I had to re-read, but you said rec/drier, and for some reason GM went backwards to a P.O.A system with Expansion Valve.
My 78 has a factory CCOT system whilst my 87 & 90 also have CCOT. (C4)
Expansion valves or at least externally adjustable ones allowed you to set the temp of air out of the vents, whilst CCOT rely on mixing hot & cold air for the desired effect. Both systems have their devotee's.
As Sirfixalot says, you must ensure no holes in the fire wall. As soon as the car gains forward motion, a reduced air pressure or partial vacumm is created within the cabin, which will suck the red hot engine bay air directly into the cabin and you will then complain like many corvette owners before you, that Corvettes are mongrel hot cars to drive.
STD from the factory they are insulated, underfelted and carpeted. There are also sneaky bits of closed cell foam blocks & strips that seal around the radiator, the transmission to trans tunnel gap etc. Once your A/C is running and the car sealed you will be driving a cool quality muscle car and enjoying it.
I used similar material to Sirfixalot, a thin insulate with al-foil backing, self adhesive with peal off backing, easy to use, cut and shape and mold around everthing. When I first did my 78, I sealed 30 odd firewall holes (fglass epoxy), then did the insulation, underfelt and carpet, the car transformed overnight, restoring the A/C was the icing on the cake, no more foggy screens etc.
P.S some early Comodore (VB ~ V?) Parts like the Dash controll are either direct replacements or have similar parts.
Cheers.