I had a brain f*** when composing my reply. Tried to correct it with an edit but was too lazy to go back and change a bunch! Threads are clearly the same but when you open the MaxAir screw one turn it's the equivalent of opening the Mikuni screw two full turns or at least that's what I've read and been told. Seems the needle on the MaxAir doesn't have quite as gradual a taper as the Mikuni.

On your other point... I bought a spare Mikuni thumbscrew, mounted it in a pin vise which protected both the threads and the business end of the screw, and drilled it out with a 1/8 inch cabide drill bit. (Had to use a carbide bit because the screwdriver slot in the top of the thumbscrew would cause a regular bit to wander.) There's not a lot of brass in the top of the screw so you have to be really careful when drilling. Then I JB Welded a small length of .1 inch aluminum welding rod into the hole using the drill press as a clamp to hold it perfectly vertical. Mounted a small length of 1/4 " knurled rod on the end of the rod to make it easier to turn. Seems to be working ok so far.