1976 Brakes convert from Hydro boost to vacumm boost

[Jamies57]

I have an Australian imported chev C30 long wheel base dually Ive converted an early international body onto it in COE form now its time to fit brakes, The old Hydroboost system is too bulky to fit in its standard form so I am going to fit a remote vacume opperated booster and master cylinder. The Hydroboost on my truck has the 1 5/16" master cylinder but all the after market master cyliders seem to be 1" Does anyone have any advice on what after market master cylider or piston bore size will actually work on this chassis? Any help is greatly appreciated

Jim