Mine’s a UJ-857D, the firmware is KBVB (after the recent upgrade through software update). It’s stayed KBVB after the hack.
I got worried because the first thread I read here I misread and started out looking for Macbook Pro firmware. Luckily I worked that one out before I did anything stupid.
With regard to what’s in your machine, if DVD Info agrees with the System Profiler, it’s probably a UJ-857, but if you’re not sure don’t touch it. I’m sure you won’t, but I had to tell myself a number of times earlier, it can’t be said too often!