All the various manifold I have seen I usually tapped below the carb, in the flat area away from the engine. SOme have the smaller holes others like my 261 truck manifold have the larger 6 sided brass connector that allows PCV hook up.
Problem is I have to remove my connection brass block and install a flat pipe plug.....because the COE desing I am working with has barely 3/4 inch clearance between manifold and engine cover sheet metal.... less 1/4 inch for the insulation pad..... hood opening is about 15 inches by 22 inches.... an absolute nightmare.
That adapter was used for connecting to a period brake booster which I have located and will eventually install... it is an early vaccum assist booster remote from the master cylinder.
Gotta find one or have one machined....
Thanks for the comments...keep them coming..
Bob