Before you invest too much time or money, you may want to take a look at this:
YouTube - Airdrome Aeroplanes operating machine guns
Granted, this is a Vickers, but I think he mentions a Spandau also. It wouldn't be much of a leap to build one.
I'm not trying to discourage you or anything... however, if you build yours... what will make them different from these?
I was hoping Robert would bring these to Gardner, but he didn't.