I have removed those bolts with a offset boxed end wrench. I'm in AZ so not a expert on removing rusted bolts but when I am trying to remove them I use a little oil on them. If they break free I keep adding a little oil and then tighten, then loosen until I get them out. On bolts like the sides I use another nut to clean the exposed thread before trying to remove the bolt. Again using a little oil. Found the bolt will break free only to lockup and snap off after getting on the **** from expose thread into the fixed nut. I take it you are leaving the front door headers in place or did you take them to remove? On the rear header make sure you don't have another bolt on each side of the header that bolts to the end of the sides. I haven't done this in a while but I believe there are a couple of bolts that go into a flange off the header that bolt to the top of the sides. The drip rail has a larger hole so these do not have to be removed. But like I said there may be one that does need to be removed.