I used Currie's on my D-300. I like it. I've got to carry a cheat sheet to know what range I am in [img]images/icons/smile.gif[/img]! I like the thought of if I brake a rear drive shaft, I can still crawl out in front wheel drive.
If you don't modify the D300, then correct you don't get Hi-range front only. You have to take a ball bearing (I know its called something else) out of the shift rail house that prevents you from putting the D300 into that range. You do get Low range front only, if desired. (same as the d20 twinstick shift pattern).