The best bet would be to get the serial number and call Bryston and ask Mike Pickett.
My B60 is dated 9932, which I believe was very close to the time they changed over. There was something posted here that said it was an SST, which is what the seller and I went by. Unfortunately it wasn't an SST. I have since sent it to Bryston and had it upgraded for about $125. I mention this because if it isn't an SST, I'd imagine that you could have it upgraded for about that price. I'd get confirmation from Bryston regarding SST status, and confirmation on price of the upgrade if not.
James will probably chime in.