Afghan, which is already in the game, and Bactrian aren't interchangeable, but Afghan is pretty much the continuation of Bactrian culture into the middle ages. If Bactrian were to be represented, it would probably be best through the Afghan, which represents the merging of Kushan, Hepthalite and native Bactrian cultures. On that note, Afghanistan would be mostly Buddhist in this period and Pakistan would be entirely Buddhist. Not sure about Balochistan, or if there was a distinguishable Baloch identity at this point. You probably know this already but India is going to need a lot of work.