If you do get a Rev C fully working, would be cool to see pictures.  No surprise that KnC was wrong yet again.  Still, a Rev B is a cheaper alternative if you can source one and it works just fine. As far as I can see, Rev C just has more onboard memory and some software/GUI improvements that I doubt will matter on a KnC miner.

I did peer through my Mercury's case and finally saw its BBB Rev, it is older. Here's all of mine:
Oct '13 Mercury: Rev A5C - PCB Rev B4
Batch 0 Neptune: Rev B - PCB Rev B6
Batch 1 Neptune: Rev B - PCB Rev B6
Bonus Neptune: Rev B - PCB Rev B6

So you might get an old A version with an old October Controller, not sure about the November boards. I think this Rev A change: "Changed C24 to a 2.2uF capacitor. This extends the reset signal to solve an issue where some boards would not boot on power up." is why the BBB in my Mercury doesn't always boot. Not worth replacing though, I just power cycle until it boots and that's worked fine for well over a year now.