I could be wrong but I don't think I'd want to attempt to circular interpolate a .0004" bearing bore tolerance. Think about roundness, size and bore taper due to cutter deflection. If this job has any volume to it, you should get a holder. If low volume or low repeat, I'd make up a boring bar that's adjustable with a screw and set it with a high accuracy (.00005") dial indicator.
Or get a relatively inexpensive Critereon boring head that will hold tolerance.