Will stock 04 GT springs work on a Fox?

The exact height difference will depend on the options in both cars.
Do you have an auto/5sp, AC/no_ac? What were the engine, tranny, AC, etc options from the '04?
You do realize that there are a few different engines and tranny options for an '04, right?

So. anywhere from stock height to ~1/3" higher depending on the exact options in both cars.

If you need an exact number: 0.250000" +/- 3.5334". :)

If you want, you can cut ~a thumbs width from the '04 springs. You cut the same amount on each spring by width (e.g. number/percentage of coil). You never ever cut by height.

See:
Cutting stock 1993 5.0 springs - Corral Forums

FWIW, when you read "cut a coil" from the front springs, you know that either that person is repeating what they read, or their brain is so fried from drugs, they have zero touch with reality. If someone really cut a full coil from the front spring, the spring wouldn't do squat.