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Erik, I do not have any pics since I did not have my I-pad when I tore apart my 77 K10, but I did write and draw everything I possibly could in my handy note book. So I will see if I can answer your question while you wait on some pics. Standing in front of the truck, looking into engine bay, down on top of the charcoal canister, you should have 2 ports on the 77. The right port, went to the carb. to the bottom small hose & to the right of the big vacuum hose. The left port goes to frame by steering box, then the rubber hose is connected to a metal tube that goes across the front of the truck to the passenger side as you described, (except the part of connecting to the front pumkin), it went all the way to the passenger side and turned and maybe had about 6" or 8" of hard tubbing. On my 77 K10, the metal tube ended on the passenger side and a rubber line went to vent the fuel tanks, not a hard line. Hope this helps, and sorry I did not have any pics for you.
Glad to hear your making progress! Don't forget the checkbook when you go to fill the ole girl