Those Duncan-designed Squier J pickups were really nice, they punched way above the weight of the pickups typically found in instruments like that (and much nicer than the pickups Squier replaced them with when the DDs went away, heck nicer for my ears than most Fender J pickups I've tried). I've actually replaced some boutique J pickups (Fralin and Nordstrand single coils) with DD sets and preferred the DDs. I've accumulated a few sets though I end up selling them in cheap project basses like a dummy, they are harder to find these days than they once were! (I still have one set or maybe two and won't sell them again). From my memory, the DD Duncans were very similar to the Duncan SJB-1 pickups like the OP has- just a made overseas take on it.