Vacuum Squeal?

[Droff]

I've got a 350 with an Edelbrock 1405 carb. I haven't had any noticeable problems with the truck starting or running but it has been sitting for about 6 months until I started her up yesterday. Previously, I had noticed a sharp squeal when getting on the throttle, this is just sitting in the driveway, pushing on the throttle. Yesterday, it was a bit worse. Very loud squeal, actually sounds like a belt slipping, and only at initial quick throttle.
I think I have a vacuum issue due to where it sounds like it is coming from but not able to test the theory yet. I'm going to pick up some starter fluid and see if I can find out for sure if I have a vacuum leak. I've tried to find pics of the back of the carb so I can make sure what connections I have but not having a lot of luck. The pic is the back of my carb.
The large port on top looks like it is for the power brake booster connection (which I have going to the intake). I can't find what the port underneath it is, it looks like an air hose fitting on maybe an adapter plate? Just wanting to make sure what vacuum lines need either connected or blocked off.
Any help?