Tom,
I'm not sure if you're aware, but going by recent discussions on the Mach list, Brian is not making the plugin interfacing information public domain for Mach 4, so you may want to contact him directly to ask.
There is talk of a Mach4 Mill beta release within a week, which already has plugins tested for Parallel Port, ESS and Hicon, so the information does exist. There is also talk of a Mach 4 Turn beta not too far off, it's just Brian wants to run it on his own lathe first!
Moray