throttle shafts can be pre pressured , done it with press in tubes (brakeline)from the sides and sandwich plates below , i like the sandwich plate better
just have to drill a port from the base of the carb to the throttle shafts and get your air supply from a pitot tube pre carb , it will have a little more pressure than internal carb pressure and although the shafts don't seal any better they only blow out air
same air supply point can be used for referencing a mechanical fuel pump , put an air fitting in the breather hole below the pump diaphram and be sure your shaft seal is good