Yes I thought of shaft couplers you can get quite fancy bellows type wich look as though they might be best although quite a price too. but ive tried to avoid them, as they must reduce the overal torsional stiffness to some degree,
Ive glued the bearings in place in situ so it should be aligned and this has helped. removing the preloading also helps a lot with the error cuased by drag but the play in radial ball races without preload is then a problem.
Colin =^.^=