The 11x2.5” finned rear drums shouldn’t overlap the backing plates. If yours do, you’ve got a problem. Same with the axle stand off and the green bearings, you already know that you shouldn’t have to run a washer as a spacer.
Almost sounds like you’re running SBP axles re-drilled for BBP instead of actual BBP axles, the flange offset is different. Or Moser axles with the SBP offset and 5x4.5” pattern.