First slant, multiple questions

That hose (it's the carb bowl vent) should go to the vapor canister, usually on passenger side behind the headlight, about the size of a coffee can. Look for a Vacuum hose diagram somewhere in the engine compartment (if it's still there). You should rebuild the carb, or at least spray it down with carb cleaner to figure out what is leaking. There are a couple of 1 bbl carbs for sale over on the .org site as well. If you don't know the condition of things, you should just give it a tune up, plugs, cap, rotor..at least the basics. It wouldn't hurt to adjust the valves and set the ignition timing. It is very hard to kill a slant six, but that doesn't mean it won't run like crap if you don't take care of it.