1969 Dart rear quarter cut outs

Looking at the picture, if you cut it where he has it laid out, the forward cut would be inside the car. I think it's WAY too big. In my opinion, that pattern isn't even close.
Having seen real LO23 cars in person, the forward cut ends up putting the wheel well flush with the cut line. In other words the cut in the quarter would be flush with the wheel tub at the forward edge.
Once it's cut, you can weld a return flange to the quarter skin, and weld it to the wheel well for a finished look.
Keep in mind the original Hemi cars were not very detailed in this area, and was kinda crude looking.

George