I've previously owned an 03 Mach which was on Maximum Motorsports coilovers (lower than stock) and I can tell you that the GT350, stock, is lower than that.
That kinda suprises me. If I remember the Mach1 is higher than the Bullitt because of Gov regulations and the Mach1 was as low as they could go legally. So I'm a bit surprised a GT350 is lower than a lowered Mach1.
There is more going on than simply height. The distance the lip extends from the wheel centerline affects how soon the lip will make contact with the ground with relation to the angle of the front of the car. While I have not owned a Mach 1 I have had several lowered cars with much less clearance than the Shelby and had no scraping issues but those cars did not have a front end that had as much overhang, cantilevering the splitter so far forward. It definitely makes it more of a challenge and makes it impractical for me to lower the caras much as I’d like to.