There are a few tricks for aligning throttle shaft, throttle plate, and throttle arms before drilling the shaft for the retaining pins. The idea is to reuse the original hole in the lever, and have the lever positioned properly so you don't run out of adjustment for the throttle stop or the idle speed screws.

To properly align the idle levers, install butterfly plate in the carburetor using a new shaft. Press the plate closed to have intimate contact with the throttle body all around, then tighten the retaining screws to secure it in that position. Slide the lever onto the shaft, and adjust the idle speed screw or the throttle stop screw so there is 1/16" protruding through the lever. This assures that you will have some adjustment for assembly tolerance and for later wear. Put a drop of cyanoacrylate ester (Krazy Glue, or Loctite Super Bonder) on the shaft to glue the lever to the shaft.

Once the glue has set up, adjust the screw on the lever so that the retaining pin hole is perpendicular to the base of the carburetor. This will allow you to drill the new hole in the shaft using the original hole in the lever as a guide. A drill press is mandatory for this operation to keep the hole centered and perpendicular to the shaft. After drilling, gently tap the new pin into position to permanently secure the arm to shaft.

On Nov 3, 2023, Rob Zucca in Camarillo, CA, USA wrote:
"Measured a new throttle shaft pin. They have slight linear grooves so they bite into the drilled holes. They measure .116-.118. Also shown is the drill bit I’ve used for a few sets of carbs. New shafts from Moss etc. are from Joe Curto and have roll pins of the same size. I’ve used original pins as well as roll pins and they’re the same size".

That is a #32 drill, 0.1160-inch diameter.