Last I heard Jake Raby was the US distributor for Subygears. I have a few sets of their 4WD to 2WD parts in stock for a project we are working on, but you can't do that box on Tom's chassis.
In one of our new projects we'll be using the Subygears stuff, but in a mid engine configuration.
I am waiting to hear more about the rear engine setup, but it is my understanding that the reverse cut ring and pinion effects the way the oil is slung and can possibly starve 5th and reverse. I don't recall where I read it, but some guys had pulled their boxes apart after failure and those gears were blued!
I don't know if Jake still frequents the forums but if he does maybe he can comment on that, as well as his involvement with Subygears (if he still is).
On our "Suby Spec" VW boxes we have Rancho build the "best of the best" gearbox at almost $5K with a full custom Weddle gear set to match your engine's hp/torque.