hello guys. just did this to my 1981 ford f-150 custom w/o a/c 2wd manual. yours might be or might not be same but this is intended to show a general uninstall of the assembly to get to the heatercore or blowermotor. i dont know if i did it the right way but i got it done so i took some pictures as i was going through it myself.
Under the dash:::
1) take out glovebox
2) Three washernuts you have to get to
1)remove cowl panel to get to upper left bold. (mine had a nut in the back of it.)
a series of screws along the rubber stripping (8) and in the vents them selfs (4)
2) do a reach-around to the bottom and unscrew the lower left bolt.
3) unplug fan and resonators.
4) take off wiper blades
before i put it in... i took the time and wirebrushed all the rust off the heatercore frame and sprayed it with some rustcap and blue for ford!
this is new heatercore installed.
this is with the newly sprayed frame installed.
now i put back all the 7/16 hex head screws and tighten everything up...
then back into the firewall... same way. i put all nuts and screws in lose then tightened everything up when it aliened correctly. (this step is easier then uninstall.
I have an 81 F350 without AC and did something kind of similar last Fall.
Mine was leaking where one of the tubes is soldered into the tank, I used a torch to heat
up the solder joints so I could remove the tubes, cleaned everything up as best I could, then
soldered it all back together.
But I also glued some foam rubber to the flap(s) in the box, the original had dry rotted and
turned to dust when I touched it.