Got the ducts swapped out, it was NOT a linear process ;-) Not much room or light, so few pix worth sharing.
This first one demonstrates the legendary Chevy craftsmanship with stalactites of seam sealer.
Just to get the old hose pieces out and gain access, I had to remove the Glovebox cover, the glovebox itself, instrument panel, 5 vents, and the heater/AC control panel.
I needed two hands to get the hose onto its fittings, so had to pull some pieces out connect them, then put them back. To remove just the fitting at top left, I also ended up removing the radio and speaker.
I had bought a set of replacement(unmarked) hoses which all worked out for diameter and length...if not always on the first try, but some fit tighter than others. I improvised some baling wire hose clamps to retain some of the hoses to their fittings, since I felt it would hold up better than duct tape or zip ties over time and heat. Surprisingly, the plastic vent pieces were not brittle at all, and snapped in and out of place cooperatively
The speaker cone was the consistency of a dry leaf, and the cardboard glovebox didn't survive extraction, nor did the wiper switch, which was apparently held together entirely by grease at this point.
Also swapping out a broken defroster lever, floor duct, that had succumbed to the ravages of time.
Dash pad goes on next