Nick,

Moving the buckle/strap is not difficult. It is usually good for an inch or two, but not much more. The strap on the under-apron is moved toward the center, as someone has said. The buckle on the right is moved toward the back. Often the hip strap is OK where it is, or you can remove it. :-)

The results depend in part on the cut of the kilt. For instance, I think a Stillwater standard or heavyweight in 30" would do well for you, since their apron tends to be a little on the narrow side of the traditional cut. I'm between SWK sizes, and I have one each of an inch smaller and an inch larger. After moving the strap/buckle, I like the one-inch-too-large one best.

My SWK's had the buckles sewn into a pleat seam, so they had to be removed carefully and the pleat repaired. I put them back in the "normal" way, hand stitched from the top.