Agree w/HRL, the big hole looks to be tapped into the intake's fuel/air plenum, you should be able to either shine a light into it and see the inside of the runner or poke a soft prod around to determine it's in the air plenum. The small hole looks to be the hot water tap into the much smaller & separate heat chamber below the fuel/air plenum.
Vacuum will be present in the fuel/air plenum and not in the heat chamber. If you have vacuum in the heat chamber your intake manifold is bad.....

Another note on bridging a PCV and vacuum wipers together. The size of the PCV (amount of vacuum it passes) has everything to do with whether the wipers will work. Size the PCV too big and the wipers no workie. The PCV has to pass enough vacuum to be effective yet not steal so much of the vacuum that theres not enough to operate the wipers. Dual carbs add's to the complexity.
You will probably have some trial and error before you get a good combination and as HRL suggested a vacuum reservoir will probably be necessary.
I ran a PCV on my now retired 216 with vacuum wipers for several years without problem but it was a single carb. It can be done.
Good luck
Dave

1949 Chevy 1/2-Ton 3100
1949 GMC 1/2-ton 100
In the Stovebolt Gallery
More pix on Photobucket
Video of the 216 running
Video of a Winter Cruise