Yeah, it makes sense that maybe the carb was a later carb and the EVAP (charcoal) canister is the original. And that the electric choke was removed and the fuel bowl vent was capped.
Yeah, my hose was pulled off the metal line to the tank right under the hood hinge. The first emissions they controlled was the fuel vapor that escapes into the atmosphere and stinks up garages. The fuel tank first the vent in the cap changed to a one way vent, then it was unvented and the EVAP canister added to capture the fuel vapors. The carbs were also vented to the EVAP at some point, but from yours it looks like maybe that happened later. And of course the blow-by vapor in the crankcase which the PCV valve was added to close up the crankcase so it didn't vent to atmosphere.
So you have three places you might smell fuel vapor from. The carb which now has an open element air cleaner, so fuel vapor in the bowl just leaks out there. The valve cover breather which used to attach to the air cleaner so vapor would go there (probably not much when engine is off). And of course the line from the fuel tank to the EVAP (charcoal) canister.
I'm still trying to find a diagram for your hose layout online. I found another one for my year which is a pretty good one showing how the top of the EVAP canister looks different, and the THERMAC line attaching in the same spot as the vacuum advance line (front of engine is to the left, driver side is bottom).
Oh, he had the head off too? Probably used the standard rebuilder gasket with 0.040" thickness, which means your CR was reduced. Aside from the radiator swap and the factory carb rebuilt, my Camaro was completely unmolested. Although they had switched the vacuum hoses for the EGR/EVAP and THERMAC around, and switched the #3 and #4 spark plug wires. But I caught those goofs before I really got it running again. Good to have the factory assembly manual.
Ah ok, that heated spring in the manifold sounds like a similar setup as what they did for the 2bbl V8 with the 2GC carbs. That's why it wouldn't need the electric choke. My guess is that the difference between your layout and mine occurred in 1975 when they introduced the catalytic converter and the integrated cylinder head (intake and cylinder head combined into one casting). But 1974 may have had some of the changes due to the HEI as well. I gotta find some diagrams to see when they changed what. I find the running changes really interesting.
GM only use full manifold vacuum for their HEI. I'm not sure if the placement of your points vacuum line is full/manifold or ported/timed vacuum. It's a little higher on the carb body, while the EGR port is low on the throttle body base. The spot where your EGR is plugged in is where my vacuum advance and THERMAC hoses are plugged in. So maybe you should repurpose that port for your HEI when you swap to make sure you have full vacuum. But mine also has a distributor TVS (thermal vacuum switch) with a delay valve attached as well.
Two things I am not seeing on your engine are the EFE system and the heat stove on the exhaust manifold? Does your's have the EFE flapper valve on the exhaust manifold that redirects exhaust to the bottom of the intake manifold during warmup? There should be a vacuum canister that actuates it and a vacuum port for it on the manifold? Maybe this was a later edition too, and the intake heating was just passive on yours? There should also be a metal shroud attached to the exhaust manifold with a round fitting that a rigid metal tube attached to and then ran up underneath the snorkel of your air cleaner? The flapper valve in the snorkel has a vacuum hose that runs to a vacuum switch in the underside of the THERMAC air cleaner and then a second hose to a vacuum port on the carb? You said you had a mystery hose on your air cleaner, so I assumed it was to the THERMAC flapper valve in the snorkel? Unless maybe you were talking about the hose that runs to the breather filter in the side of housing that used to connect where your valve cover breather is now? Take a pic of your air cleaner and I can tell you which hose it is.
