I have seen pics of one other with DT, but they are scarce/odd. Well worth keeping.
Does it have Browning markings on the frame or just on the barrels? Could it be a Miroku 500 DT frame fitted with a set of Browning BSS barrels? All matching serial numbers? I have never seen a BSS with factory case coloring, but have seen a few Miroku guns with CC. Can you post pics?
splinter forend and factory sling swivels
That part sounds like a Miroku configuration. The BSS Sporters all (or maybe not) came with a slim beavertail and oil finish. What's the finish on your wood?