To be honest if you have turned the pantographs round ok then I doubt anyone will notice the roof unless it's sat alongside a RhB one. Maybe remove the block towards one end if it will unscrew and put it or a fabricated replacement in the centre.
Good luck with the chrome, I hope it's thin enough so that it will stick at the corners as it's the crease that usually makes it lift off either side with thicker vinyl. Might be worth testing a bit on a angle made out of scraps of plastic first.