Sorry, total brain fart on my part.

The PV gets its signal from that hole at the bottom of the cavity, into a hole in the baseplate,(just like yours), but the hole in the typical “universal carb” baseplate has a little “v” channel to get vacuum when the 4 hole gasket is used(see pic).

I don’t know what I was thinking about with the cavity in the center of the carb and the PV

(Looking at your pic with the 4 hole gasket in place...... it still doesn’t appear as though the gasket “sealed off” that front cavity.
It would only need a leak with as much area as the size of the hole from the base into the PV cavity).

You sure those extra screw threads from the bottom aren’t interfering with how the PV slides into the cavity?

You could still try plugging the PV.

Measure the PVCR, calculate the area.
Calculate the area of the current primary jets.
Add the two areas together.......calculate what size hole that equates to..... install jets with that size hole.
That’s as good of a starting point as you can get without wet flowing the carb.

You should check the gasket surface for flatness on the front and rear of the main body.
I’ve seen them pretty warped in the past, which caused all kind of problems with several aspects of the carb function.

“Back in the day”........ when we’d send carbs out to have them “done”, milling those surfaces was always part of the process.