As I mentioned, I have cut the original rolla into three sections, shorter than the original. I inserted two disks cut from scrap plastic. (The disks were cut with clippers to make a cog/saw blade shape).
Here's the turret for the Flakka Trakk.
It is made from a 1/48 model kit of a KV-1 tank (the WW2 Russian tank with an absurdly large turret), pieces of brass tube and spare bits of plastic, including the aerating tube from an aquarium. I decided that building a turret would be simpler than assembling firing mechanisms for four flakka guns. I will add hatches, battle-damage, grot loaders and other details. I still have to figure out how to mount it on the truck bed of the Flakka Trakk vehicle, so that it has some clearance over the cabin.