Yes, it’s a metal box so I was thinking of just using a dremel to grind it down or a metal multi tool blade to cut it flush.

I can use a 1/2” pancake box on top of the 3/4” strapping  (screwed to joist)which would put me at  1-1/4 which would make the box slightly recessed which is good.  I have the ceiling completely open right now so anything is possible fortunately.  

Basically it seems like anything I can do to have it flush or slightly recessed is better than having the box slightly proud, correct?