The JC 120 is 2 channel with independent EQ's, 1 channel dry the 2nd channel reverb,chorus ect..
The head if I remember correctly is just the 2nd channel with the reverb,chorus,vibrato..
It was a great (clean) amp before it had a loop. I used to have an early one that had no loop IIRC. It was stolen many years ago. The one I have now has a loop though.
I think both channels on the combo are the same, mirror copies. The real joy was when you kicked in that stereo chorus, very lush. This amp had its faults for me, but I enjoyed running a good pedal out front and stereo return, very spacious.