I know, shame on me for not doing this when warmer,
but now I need heat. There are only 2 'knobs' ( fan / air )
of the 4 slots - but I only see 3 shafts - 1 shaft missing knob.
All I need is to manually somehow get hot water
thru core so I can have defroster. Blower works ok. (just cold air)
I have the 1½" shop manual, but some of those over-xeroxed photos
and diagrams aren't much help.
Do I start on the engine bay box on firewall where those ¼" head screws are,
or start up under the dash ?

Thanks guys ...

1960 C20 Platform