Today I started to cut out the pasenger-side floor pan. First, I made some measurements from the tunnel to the bolt holes alongside the outer edge of the pan, and from the support structures at either end of the pan to the first bolt holes on the side. This will hopefully allow me to double-check that the new pan is installed correctly, both front-to-back and from tunnel-to-side. If I cut the new pan, say, too short in the front, or if I install it too closely against the tunnel (or not close enough) then maybe I'll have trouble lining up the bolt holes when I go to put the body back on. Or, the seats will not be in the right place, and might interfere with some other structure in the car. I think the pan would have to be off by more than an inch in either direction to cause problems, though, so some moderately accurate measurements should help me keep it close enough.
Making notes about where the bolt holes are, so they new pan can be put in roughy the same place.