finishing someone else's project, have questions

Hi everyone, I'm new here. Anyway, long story short, I'm trying to get my old truck running that was left only half-finished by someone else. He had put on aftermarket intake and exhaust manifolds and bought an HEI distributor. I got the distributor installed and wired in so now I'm putting the carb back on. When I was trying to figure out whether or not I could get away without using the spacer temporarily (I can't find long enough bolts), I noticed a threaded hole at the back of the intake just under the opening that the carb spacer sits on. Except for the fuel line (which obviously goes to the carb) I can't see anything in the engine compartment that would go into this hole. What's it for? Can I just put in a threaded plug? If it's for a vacuum line, where do I put the other end?

Truck is a 1971 with a 350.

That is where the hose from the PCV valve hooks up.

Or you can use it for a vacuum supply for power brakes.

If you don't need it, plug it.

It's good to see you here, perhaps when you've a chance, put up a picture of the project.