First I modded Bee's central hood flap and the underlying cannon to flip outward in alt mode. Then I just popped up the rear roof/trunklid. I need to find a small pair of guns to stick back there like the DOTM Deluxe.
Jazz was trickier. I'd already modded his cannon, removing any motorcycle parts. I just shaved a bit of the swing-arm where the wheels used to mount so it fits into the gap in the middle of the trunklid panel, which goes up over the roof. Now he carries his crescent cannon in alt mode. He will also get a pair of cannons tucked into those upper corners of his rear panel.
