hey there
I have that exact combo, and i love it, though there are a couple of things to bear in mind.
It is a 2x12, and it is indeed the combo verson of the jmp mk2 50watt 2204 head. Mine is a '78 with el34s.
That ebay pic someone sent is indeed it.
It is bloody heavy, partly because it is bigger than it needs to be - certainly bigger than most 2x12 combos you will find nowadays. It is open-backed and definitely lacks a bit of bass. I know this because i also have a 2x12 closed back cab that i sometimes use it with. It will have two celestion speakers, that are usually greenbacks. The amp is also very bright sounding and you may find yourself turning the treble sown to about 3. Like all marshalls, they only really sound good with the master volume at least above half way, and at this point it is LOUD - louder i think than modern 50watt marshalls would be. I have used a hotplate with it, but i am just not an attenuator fan - whatever you gain by being able to get more power tube gain, you lose in tone, at least if you want to play at bedroom volumes.
On the other hand, the tone is superb. It of course only has a single channel, with two inputs. If you want a true clean sound you need to use the low input. As you turn the gain up you get the most beautiful crunch sound you could ever want. It is very touch sensitive and dynamic- with the gain on 3-5, strum lightly and the sound is almost clean, a little harder and you get that lovely marshall grit where you can just feel that hint of drive. Strum hard and its just a fantastic classic rock tone. There is no horrible fizz that you get with most modern amps including marshalls. With the gain on 8 or 9 you get an excellent rock sound, though it is never gonna do thrash.
I also have a jubilee. The sound from the JMP is considerably more touch sensitive and dynamic, less fizzy, more toneful. But i have to say that when i gig, i use the jubilee, as it is easier to get around, and has 2 channels which i find easier to deal with (i am crap at using my volume pot while playing)
Also compared it to a non master volume 50 watt 1987x that the shop had in stock. I have to say i prefer the sound of the 1987x (thicker, warmer), but just decided it was not practical to go without a master volume.
Finally, id say that your idea of turning it into a head is worth considering. Of course, on the down side, you are messing with a classic piece of vintage gear. But on the other hand, with a closed back cab and the right speakers (i would go for one greenback and one G12H), the sound would be superb, and would make a great gigging amp as long as you get on with single channel amps.
