Rega P3 - Arm hole too small?

It should not be an issue if you use a conventional protractor to set the overhang. However, if you use the Rega three hole mounting scheme, the stylus will not be in the proper plane, though this mounting does not conform to the common Baerwald formulas anyway.

Just out of curiousity why would it not work anymore with a Rega protractor? I should mention I did not touch the upper surface of the the hole. The top of the whole (plinth)is the same diamater as before just about 5mm and under all the way to the bottom is where I dremeled. So 5mm under the plinth the whole becomes irregular.

Thanks again, I am a little inept when it comes to working with my hands so I just want to know if I caused any harm.

The overhang, which is fixed with the three hole mounting, is determined by the pivot to spindle distance. You have changed this distance if you have moved the position of the arm. With two hole mounting the play in the headshell will allow you to compensate by moving the cartridge in the headshell.

The arm distance pivot to spindle should be 222mm for a Rega P3.That is from the exact center of the tonearm's pivot to the exact center of the turntable spindle.Now I think you have not altered your tonearm's position from what you have said so you should be o.k.The thing that is actually more important here is how much you tighten the base nut as this has a big effect on the table's sound.Too tight and you will deaden the music too loose and the music will be diffuse.Try only tightening the nut to finger tight and then just a 16th of a turn more.Using your ears as a guide be patient as it can be labourious but try to listen for the 'sweet' spot,the sound will open out when you get it right.Yes it is worth doing.