Yep, mechanical braking. Haven't done this before, so I need to find a tutorial on mechanical brakes hen I've gotten the components (Next week I guess.).
Here's a couple of pictures of a converted GST. It looks like the guy removed the tranny and just used the center diff spur;
Attachment 9159
This is a pic of a conversion WITH the tranny;
This guy uses all the gears, and according to him it's working fine: