Replacement allen head screws are 4mm x 16mm. I know, I know, they are rusty. After the mods were made I replaced with new ones (originally had to buy 100!).
I debated whether to cut off the tab on the mixture screw or the bowl stop - too hard to cut the mixture screw without taking the screw out of the carb so the bowl got chopped.
This notch was cut with a Dremel tool using a brown cutoff wheel. Took about 20 seconds per bowl.
Finished modification to allow adjustment of idle mixture screws.