Sounds a bit archaic, but I can only imagine that the "freewheel stop" is the shoulder at the inner terminus of the threads on the DS of the hub against which the freewheel will abut when it is tightened onto the threads of the hub.
Install the freewheel loosely, or install the cassette on the freehub body (if so equipped) and stack the spacers and install the locknut so that you will have 2mm or so of locknut protruding past the outer edge of the freewheel or cassette lockring. That orta do it.................