I think he is still out there. I had to replace my right side of my 40 ford coupe, rust near the decklid missing 7 inches. I just replace all of that side. It was in the rain on pole barn side, the other was fine.
I got inside and carefully with a circle cutoff/hammer and chisle without distorting the outside. You only need just that the drip rail can slide from outside. I have never seen a 31 Graham. Gene's would probably would start with a machine with a straight drip rail. I would think your model would be better that way. Maybe just take the top off for you project, when you could easy if you understood. If it is more like a forty ford. If you send me a photo of your Graham. Grahams are really neat, if it is like a box, all you have to heat the cut/pie/corners. Use alot of clamps, clean joints or sandblast inside and use Epoxy after tacking with a mig welder. If you have curves on the rails, you will have to heat as matching with the seams. That's how I did it on my forty ford.