I a little new to this game yet but, it would be easier to size the shaft to the handle instead of handle to the shaft. If I made a custom cue for a customer who wanted a z shaft, I would just purchase a parcial from atlas and match the ring work. It would be best to sand the two pieces together for a perfect match. A finished shaft would already have a finish coat on it and the length would already be set. Do yourself a favor and ask your cue maker to get the shaft for you if you haven't purchased already, chances are he can get it cheaper.
good luck, Jim.