Love your Gillig!
I used an air compressor chisel, beastly screwdriver, hammer, crowbar, and a lot of care. This is the section that I hurt my back. The metal is awkward, heavy, and gets jagged. By far the physically toughest part of the process so far.
I'd use the air chisel to get underneath the pleated, folded-over-on-itself gaps, and creat a bigger gap. There's spot welded points that had to be cut through, and I'd use a couple different methods to do it, mainly hammer the slot screwdriver through the metal to shear it off, or the prying parts of the hammer or crowbar to rip it in two.
I got 1/2 way done, and found out that they had reversed the overlap pattern...they essentially started at the front AND the back, and met in the middle....which meant I had to start at the unfinished end and create another opening, which wasn't easy to do.
I hope that made sense....