Rob, looks like you have a parade belt that is being used along with a Zweidorn buckle. have a look at these links and it will show you what the configuration should look like
Leather Belts and who would have used them
Buckle and Belt characteristics, originals & fakes
as Ben said buckle and belt don't go together.
The shown configuration is both well documented and well known. Essentially, a cleverly designed and "loose" open gate rectangular buckle that is capable of fitting to a "loose" traditional configuation, Political type leather strap - appearing fully in simpatico.
Original and in my opinion, quite rare.