I run a manual master from a '69 Corvette. It also has a 1" bore and works great with my front and rear calipers which are Chevy truck calipers found on any mid-70s 1/2 or 3/4 ton. I'm running 37" MTR's and it stop better than the disc/drum setup I had on 33's. Many users of 4wheel discs use this same master cylinder. It is exactly the m/c that you see in most 4wheel disc conversion kits. Are you sure that you have them bled completely?