The jets are actually the same, but you get jets all the way up to 168, and 170 with the James Dean YFZ450 kit. The highest you get with the GYT-R kit is a 165 main jet. The big difference is in the custom type needles. The kit comes with two. One that is blue, and the other red. The red is leaner for higher elevations above 3000+ feet, and the blue needle that is richer is for below.
This would allow the James Dean jetting kit to be a bit more tunable than the GYT-R.