The hole will be enlarged about .10" to make room for the new bearings. It should only go deep enough to seat the bearing flush on both sides. The original sleeve that fits between the bronze bushings and the bolt will have to be turned down to fit inside the new bearings. However with the new bearings there is nothing to keep the idler arm from sliding up and down the sleeve since there is nothing outside of the arm itself to fill the gap between the arm and the brace. Therefore the original sleeve only need to have part of it turned down to fit inside of the new bearings. The rest of it should be left it's original diameter in order to fill the gap between the arm (bearing) and the brace.

Axle