i have a couple of "weatherhead" fitting part numbers that adapt the master threads to standard 3/16" brake line. they are : WHD 7909 and WHD 7912. you could then use standard 3/16" line plugs to cap off the master ports. or, you could find a junk master cylinder from a car that has the lines still connected, chop off a short section of the line next to the master fittings, then braze the line and fitting together, thus creating a plug. i have done this many times when the correct plug wasn't available, or the parts store was closed. just something to consider.