GMC Pauls has one of the best priced kits for the 6 to 5 lug I have seen. It has all the equipment to convert over to include the power brake booster(standard drop spindle or 2 1/2 drop spindle choice). Most other sites I have been on do not include the booster in the kit. $685 for it and its manufactured by McGaughy's.
http://www.gmcpauls.com/Brakes&Steering.htm
63-70 Deluxe 5 Lug Disc Brake Conversion part number 3081941
I am either going thru him when I get my 6 lug kit, or CCP. Have to decide when it come time.