Duncan,
Give me a call and I'll put you in contact with the same guy who built John White's Transfer cases for the Targa Tas N1.
He knows what he's doing and said that he and John both didn't like the amount of slip the STD Transfer Case has and he was able to modify the clutch basket to give it better and "surer" drive to the front wheels.
Honestly you're best of sending it to him and asking for a "John White Special" hahaha and the best part is he said he has all the parts he needs.