The slot spacing is the same for the Redhawk Hunter and the Super Blackhawk Hunter, so if you can find someone with either of these variants....that doesn't presently have a scope installed, you should be able to get the correct measurements.

Personally if I were going to have someone start cutting on the barrel I would probably just have them drill and tap a couple of screw holes for a more conventional mount. IMHO the Redhawk and SBHHs have the scope mounted too far forward and it screws with the balance of the gun. On my SBHH I use one of the Weigand mounts to get my red dot farther back however if I needed to have any smithing done to make that happen, I would just D&T. It will be more secure and easier to get back to zero. If you really do need to pull the scope off, it will be only 3 more screws.