I just pulled the dash from my 77 parts car. Its not too difficult. There should be a metal flange on top of the dash right under the windshield, just phillips screws.
This will expose some bolts that hold the dash in. You might need a extension
with a swivel socket to get to bolts that are angled in. 12mm ?
You also have other bolts holding the bottom in as well but are in plain sight
once the bottom plastic beauty pieces are removed. You'll have to drop
the steering column since the bolts retain it as well.
I feel that if you have to do heater core work and things of that nature it would be
easier to get to once dash is removed. Mine has air as well, (how the **** did
they cram all that stuff into there) ?? ha hah .