Hy Grizzlynaut, I apologize I gave you information for a 1/2 ton P series 1960 - 62, the number I came up with for the one ton is Raybestos part number MC21918 $127,79 at RockAuto. That master cylinder does have a three bolt mounting flange and the GM part number was 5454644 sorry for the incorrect information, I hope this new information helps.
It's a manual
4 speed with what feels like a granny 1st
