in my machinist career, as well as today, when i want something to stay in place and not shift when tightening, i use a couple of small dowels or split pins.
this will require a good pre-fitment, then precisely drilling the holes through both pieces at once for the dowels or split pins.
when doing so, it is best to drill the hole[s] undersize by .015, then ream to the correct size needed for the pins. this insures the hole is round, and the pins fit correctly as designed.
i believe this method will work for you to insure the girdle stays where you want it.
as to your clearance issues, i would feel more comfortable with around .060, but that's just me.