The output shaft bearing
The output shaft bearing is unusual, as it has no inner race.
When assembled, the bearing is self-aligning. Don't be overly concerned if the sleeve gear seems wobbly when fitted to the bearing. This movement will go away when the mainshaft is fitted.
Finding a replacement can be tricky, as the cheaper variant has an ID of 31.5mm - which doesn't fit. There are also variants with 9mm rollers which don't fit. You need SKF RNU205 Single Row Cylindrical Roller Bearing 32x52x15mm with 6mm rollers.
The correct bearing is available from the AJS Matchless Owners Club spares scheme.