I found these over on Pirate. It seems that Freightliner offers a D-70 rear disc brake set up in their utilimaster step vans. It could possibly be a source for stock appearing rear disc conversions or replacing the whole rear for higher gearing and better brakes.
http://www.pirate4x4.com/forum/showt...ana+70u&page=5
Pretty informative posts. I never realized there were so many dana 70 variants.