I would really hate to see the Mjolnir with anything but a single primary beam weapon and two secondary launchers. I believe the RBC was designed to be a stationary beam cannon, not a warship without an engine.
The decision not to include turrets anywhere, including the tail end of the unit, was a concious one. Turrets anywhere but on the aft side of the RBC do not make sense. The outer and inner grinders rotate in opposite directions, leaving only a narrow cylinder in front of the RBC clear. In all other directions, the grinders occlude a turrets FOV.
If someone needs extra fire power around the RBC, they can always drop some sentry guns or even assign a wing of fighters to play nanny.
Galemp: Though it hurts my pride, go ahead and change the geometry with respect to the secondary launchers and the lens. The original model has a the lens, lens collar, and main beam core seperate parts anyway. The back, however, I'd hate to see changed. I like the proportions the way they are now. The reason I didn't include cutouts on the outer grinder was so I could ditch the detailed machinery in the rotation hub. There's really no need to see any of the stuff in there, I think.