What are you needing additional manifold vac for (besides brake booster)?
You should have a smaller manifold vac port on the carb base on the front (likely passenger side) corner.
Usually 2 are there. Careful, 1 is generally manifold and the other port or 'timed' vac.
If you don't have the manual for the carb, throw a vac gauge on real quick to determine which is which.
I have a RPM Perf as well and a double pumper and mine is blocked too.
I hooked my PCV line to the smaller manifold vac I mentioned & it works fine.
Another option is to thead a low profile 90 deg NPT fitting in the one being blocked and with a little carb spacer (perhaps 1/2 - 3/4") it should raise the carb enough to get the clearance you desire.