help with tuning an AED 750 Ho

Get some .125 or 1/8" length cup tip set screws and run them into the current hole. If they stop above the surface, you are OK. Figure out how many more threads you need to run in to get them down/flush. Tap them incrementally until they are flush.

If they get flush and don't stop, you'll need to either go up to the next size or score the brass.