Vacuum Secondaries

Lots of good stuff here!
I'd take the whole assembly off and check the cork gasket first.
I think if you push the diaphragm rod into the closed position and hold your finger over the hole, it should stay in if there are no holes in the diaphragm.
and by applying vacuum to this port you should see it move in and out.
Only if it passes these tests should you look at the spring.
Sometimes the color on the springs has faded, so compare the old spring with the ones in the kit by stacking them and seeing which one compresses more.
That will be the softer spring. Many of these carbs came with the "plain" spring, which is kinda stiff for a light car. There is also a check ball that can be removed which will also affect the opening, as will the size of the vacuum port, but drilling this should probably be left to experts!