69-70 B body masters can vary with the lines inboard (facing the engine) or outboard (facing the inner fender), usually the 1475 power master disc application is used on the dual diaphram Bendix booster, the 1404 master you'll usually find on the Midland Ross single diaphram booster,....but not written in stone, if your lines are outboard (facing the inner fender) use the 1404 master, I usually prefer Fenco (avaliable at AutoZone) replacement units, quality rebuild and the correct master in the box


Mike