Ok. I think theres a lot of misleading information in this thread, actually, this whole thread is misleading.
6.17 gears are supreme drag gears for a car that has wide gearing and a high rev-limiter(like 8000rpm). Why is she going to swap out her Mach 1 motor for a Cobra motor ? If she's talking about getting a newer Cobra motor that's supercharged, then anything more than 4.10's or 4.30's is going to be too much on the stock tire size. If she runs a 28in slick and her rev-limiter is set for a good 7k rpms, then she can get away with 4.56's and nothing more.
I think whoever started this thread should not have to begin with. Chances are this girl is not even reading this thread so this information is pointless. It's just a bunch of guys posting thier opinions on a stupid topic and it's doing nothing but taking up space and eating up bandwidth.