What you're trying to achieve is not practical with one printer. Basically, each print head would have to have it's own operating envelope (working area), unto which another print head would not enter.
Something like the Photoshopped image is in theory possible, but the problem is you'll be left with very little operating room per head. You can't really use a multi-nozzle head like the Kraken because the nozzles are too close to each other, so you'd have to decide what the largest piece is going to be and space the nozzles apart by that dimension. What you're left with (if anything) is your X movement. Y is not a concern in this design.
You could also try a dual X gantry, for a 2x2 configuration. This would give you more room, but not that much.
Then there's the logistics behind the whole thing. Like weight, load on the stepper, calibration, etc. Z calibration in particular will be problematic, as the odds of all the nozzles being at the same height are pretty slim, so you'll have to devise a method to adjust the height of each nozzle individually.
Me personally, if I had something to do like what you're going for, I would probably buy a few small, inexpensive 3D printers and have them do their thing. For example you can buy the PrintrBot Simple, and get the job done. Each has a 4"x4'x4" print volume which should be more than enough for your needs.
FYI, going to a "traditional" dual print head, won't allow you to do what your trying to do, however, it will increase your print speed, because you can get the printer to print with both nozzles simultaneously.
To print or, 3D print, that is the question...
SD3 printer w/too many mods, Printrbot Simple Maker Ed., FormLabs Form 1+
AnyCubic Photon, Shining 3D EinScan-S & Atlas 3D scanners...
...and too much time on my hands.
