Yes, looks like a 610S.
The 312S and the 610S are both nominally 6 ohm cabinets. Closer to 5.3, the way most people calculate impedance. The original silver and black Concert series amps were rated down to 4 ohms. I'd think long and hard before running two 5.3 ohm cabinets on one of those. The later black faced, red knobbed Concert series were rated down to 2 ohms, but consensus seems to be that they can't really handle that long term. however, two 5.3 ohm cabinets works out to 2.7 ohms, which is a bit higher. I'd think they could do it, but more knowledgeable people might say I'm wrong.
So, which one ya got?