KiwiEngineer, sounds like I need to hook you up with my Kiwi mate Andrew Beck. He has done a lot of big retrofits and sells some machine tooling on his web site which I've forgotten the URL of. He can set you up with some well priced servos and no doubt help you get them going.. I'll see if I can dig him up for you.
But be warned, he'll probably talk you into using Linuxcnc because thats what he uses and he's just been appointed the Mesa Electronics distributor in our region. They make a whole range of amazing CNC controller boards for Linuxcnc.