Rocky the needy squirrel here.

First off, my apologies to all who were trying to tell me that the
heater box's footwell air control cable cannot be replaced from below.
Graham Janson kindly sent a nice photo showing the problem. I took it
over to the mechanic and he said, "Yeah. The heater valve can be
replaced from below, but the dash has to be pulled to do this one." He
might not be the best at communicating, or I might have missed this, but
the dash has to come out.

Since the dash has to come out, the heater core might as well be
replaced. Who has new? 1984.

And the heater box's flapper things don't close very well, I've heard
that this is caused by rotted foam seals. Are those seals available? Or
can someone point me to how others have jury-rigged their replacements?
Weatherstripping or something?

Thanks all, for the help.

--
Rocky J Squirrel
'84 Westfalia: Mellow Yellow ("The Electrical Banana")
'74 Westrailia: (Ladybug Trailer company, San Juan Capistrano, Calif.)
Bend, OR
KG6RCR