Here's a few photos I took a couple of years ago while I was modifying my valve for regulating a 22 Rrod. I don't remember everything as it unfolded by I think you'll get the jist of what I did.
I did Loctite or cement the velocity screw in place before I opened up the exhaust. You can see the adjuster in the port.

I then rounded off the inner edge of the exhaust port to help with flow hopefully

I enlarged the intake port to .280,

The inner sleeve of the 25cal valve could be removed at the time to allow for more volume in the valve. The drill bit's point is resting on that sleeve.

I opened up the inside of the valve further with a 1/2" bit. Care must be taken here not to go to deep and get into the seat of the valve.

This is after opening up the valve body to 1/2". You can see the seat in the bottom.

Anyway, hope this helps. I always enjoy pictures of what I or someone else is trying to explain.
There is another modification that can be done to the intake cap other that drilling it out to .280. I don't have that photo but it's just drilling a couple of 1/8" holes parallel to the .280 hole to increase flow even more.
JImmy