For what it's worth, it has been my experience, and that of other gentlemen on this forum, that when one wears a dirk with formal Highland attire the dirk belt is worn over, not under, the waistcoat. This allows one to easily remove the dirk without having to fiddle with their waistcoat, etc.

If you are wearing pumps with your evening attire, you may wish to have your local cobbler fit a bit of moleskin at the inside of the heel to keep the shoes from slipping off your feet when dancing. It is precisely because pumps tend to slip at the heel that the top strap was added to dress Highland shoes in the first place.

Do post pictures when you get a chance.