The #2 is based off of the .307 Win, instead of the .225 Win, so there is a bit more case capacity.
I guess the 6.5JDJ#2 could be called a 6.5x307 (although I think there was one of those already).
The .307 is a rimmed version, of the .308 Win. It has thicker brass, thus slightly less internal capacity. Around 10% supposedly.
A 6.5x308 already exists, its called the .260 Remington.
Due to the .307's less case capacity, you can't, of course
load exactly off of the .260 Rem's load data, although
the lower load levels is a good place to start.