1970 Chevelle 396

1st. If that Battery has been sitting there for over 3 years not being charged or or even tended to. I would be getting another battery, soon. It may work for now but it'll flake out on you in a short amount of time.
2nd. (pic is kinda hard to see) Is the Carb original or does have an aftermarket like Edelbrock, Holley, etc.?
A lot of these evap canisters are basically charcoal filled units that are designed to mitigate fuel vapors coming from the fuel tank.
The basics are usually the small steel tube coming from the fuel tank is the tank vent pipe (usually 1/4 inch) going to the engine bay, from then a small hose connects to the evap canister, and then a vent out from the canister goes into the carb or manifold. Some of canisters do have ID or letters to help show which is which.
Again I am basing this on my Duster, old Jeeps and Dodge trucks I had but the concept should be about the same.
Here is something that may or may not help you:
0900c152801daa33-3810032754.jpg