update... havent got to check with the guru yet, but asking the chemists and metallurgists around sounds like the reaction of nitric acid with aluminum is the biggest question mark. it may be more likely for low concentrations to react unfavorably with the aluminum, while higher will just leave a small amount of oxidization on the surface. im not sure but it seems like enough uncertainty that id rather not go that route.

i acquired several drill bits ranging from 1.25-1.45 mm so i should be able to figure out the diameter this evening, assuming it is within that range. not sure if the screw edge is recessed enough that the drill bit wont walk on me, but might have to do something to prevent that.

i looked at it under different lights and angles and best i can tell it is not tapered.

hole was smaller than the 1.25mm bit so i ordered 2x 1mm bits off of mcmaster (smallest they had). seemed to have fit perfectly, a little snug, i cant tell that it fit any tighter at the top versus the bottom (indicating that it was indeed a tapered orifice).

luckily the screw had broken off slightly below the surface so it left a solid holster for the bit. drilled it out with little drama, seems to have gone well. the exit shape as viewed from the throat is less than perfect, though the needle fitment appears to be well aligned. and im not sure how to check or what to do to make sure the needle valve screw mating surface is back in original shape so im just leaving it. just hope i can get this one to idle like the others...