$650 seems like a decent price these days, regardless of the revision. I haven't seen a Mark IIC, or even a Mark IIB sell for that little in a long time, so I would imagine it's a Mark IIA at that price.
Mike Bendinelli used to modify the Mark IIB to Mark IIC+ specs, but that ended quite a while ago. From what I remember, he required the Mark IIB to carry the same board as the Mark IIC+. Maybe post pictures up when you can.