Mount for the PH5C is going to be hard to find, unless you chance across one or are able to machine one up. Central, Musgrave, and others will fit on that block. Then you can find an aperture or adapter for all the modern ones. I run a Musgrave which is basically a rebranded different PH sight. (Yes, I know, Musgrave are from South Africa. Lots of stuff got 'house branded' at one time.)