FWIWm the MB.326Km with the single-seat canopy has the ammunition for the cannons where the second seat was, that's one reason it's faired over. I'm not certain how this layout affects your concept of the Prarie Rattler.
My idea with the Prairie Rattler, and other early armed MB.326 variants is to have the guns and ammunition in their real world position, but maintain the standard trainer style canopy over it all.
Partly, this would be for parts commonality between the attack and trainer versions where possible. It would also be to maintain some degree of rearward vision for the pilot.
From what I've seen of cutaways of the MB.326K, the gun package doesn't extend up past the point of the cockpit sill and the upper part is taken up by some avionics boxes.
I figure if those avionics boxes can be arranged behind the pilot so that the pilot can see to at least the four and eight positions, if not five and seven, then keeping the trainer canopy and the better field of view it could give might be prudent.
