77 Rochester ME.
If someone has a 1977 Service Manual, they could look up to see if it's for a 250 or a 292. The manual should have the vacuum hose routing (I only have the 1980 manual, so I'm not sure)
I believe one of the holes in the base is a vacuum port for the EGR system. You won't need that with your 261 so it's OK to be blocked. One of the holes in the base could be providing vacuum for the thermostatic air cleaner - probably not using that so it could be blocked.
One of the holes would be for the power piston - you don't want to block that.
