Most of the time secondary diaphragms have to be matched by comparing the exisiting. Pay attention to the length of the stem as illustrated, and the orientation of the rod hole at the end of the stem.
This style secondary diaphragm is not available aftermarket that we’ve ever seen
Be careful with this screw. They are often frozen and will strip, or break easily. If the screw doesn't move easily to start with, try heating around the outside of the screw. This will usually loosen it up.
Tighten the screw until it touches the secondary throttle lever, then tighten one more turn.
If you are having problems getting the primary idle mixture and/or idle speed just right, try turning the screw in just slightly. This will allow the primary plates to close enough to cover the idle transfer slots.
Idle mixture screws on the secondary’s and not primary is normal on some of the governor carbs, not all, but some.