Thanks for your patience/persistence, DADS 50 & Jerry
This blind man now sees the light (the tubing routes).
I now see that the metal line that goes low behind the carburetor base is connected to that black hose (that goes to a fitting near the top of a sealed tube (instead of a road draft tube)
All of this now makes sense to this thick old head.
DADS50 - I have taken the liberty of attaching and renaming your linked-to photos (in case those links ever go bad/dead).
One image (the right-most image) has been named as a vacuum line into a vacuum distributor (on a large truck). I had a multi-vacuum-line distributor on my 54/55 GMC COE. The distributor fed the following: - vacuum-assist brakes - vacuum wipers - vacuum for GMC-only complex "switch" for 2-speed rear-end hi/lo selector
