Simple vacuum canister question

[92470]

I am finishing up running all new vacuum lines this weekend and am installing a new plastic vacuum canister in place of my old original tin can one that was cracked. My truck is a completely stock 71' Cheyenne with A/C, and a 350 w/4bbl carb.

My question is from the factory, what was the main vacuum line that feeds into the canister running to for vacuum? Was it from the carb, or the vacuum fitting on the rear of the intake manifold? I know how the other hose that connects to the canister routes for the climate control system, but have gotten different answers to the main vacuum in line. Can anyone help me please? I'm sure there are differing opinions about how it should be done, I would just like to know how it was originally done. I've had a couple people send me vacuum schmatics, but none match my truck. And the factory assembly and service manuals are no help.

Many thanks! John