Looks like a BSA hub to me with a different brakeplate?
This is certainely NOT a BSA hub. BSA did make 8inch half-width hubs, of course, and in several versions,too; but these are quite different to the one 900triple has.
Main differences are: -Hub and drum were never bolted together but riveted for the pressed-steel drum or brazed for the cast one.
-If they had ventilation holes or knockouts, there were 6 or 12 of them, never 10.
-If they carried cooling ribs (GoldStar and A65), these were outboard the spoke flange, not inboard.
The Triumph GrandPrix is still your best bet so far