A frame notch is exactly that. It has nothing to do w/ the wheel well.
The notch is usually done so the outer frame face is flush w/ the wheel well.
I split the frame at the weld joint, clean everything up, and re-install the outer face into the inner 1/2. I make filler plates for the ends.
I support the rear of the frame B4 I do any cutting, to prevent sagging.
Some guys plate the inside of the frame prior to doing the mod. My car had a roll bar in it, so it was stiff enuf to begin with.
If you need more inside clearance, it's time for wheel tubs, possible suspension mods, etc.
I used 8.5" wheels w/ 4.5" BS, and 10.5 x 28 tires.