looks like a ZKB-2 indeed.
see if you can carefully lift up that beige logo? some models came with a switch under the logo (to switch between AT and XT).
if you prefer not to touch the logo, you could also see if there's something under the logo by opening the thing up : )
i wonder what that big B is on the top right of the case..? is it a sticker?
i'm also curious to the switches and keycaps : ) it's hard to see if there's any discoloration. if you decide to take a cap off to see the switches, make sure you flip the keycap around so the bottom of it shows in the picture. : )
it does look like it's in excellent shape, though!