70 Duster--conv. to 73-76 front disc??

Stainless Steel Brakes also makes kits to convert from the 10" drums to a 4 piston discs and still have 4" bolt pattern. I'm not sure if they have anything for the spindles you already have.

Probably the most knowledgeable person around on the brake swaps Is Andy F with AR Engineering.

http://www.arengineering.com/