First welcome to the site. As others have mentioned, at this site the year, model and when the car was completed is very important.
Since you left us guessing I'ld guess that this is a 69 or 70 Mustang question
If so I would suggest not looking for the distance from the rear edge of the scoop to the rear edge of the hood but rather the location of the mounting holes or at least the two rear most ones. When you purchased a new hood from Ford they typically included a large sheet that was a full size guide to how and where to cut the hole for a shaker car and a set of holes and rear cutouts for the turn indicators on a nonfunctioning hood scoop. IF you can confirm I'll look for the pattern or someone else will provide the distances