It's hardly worth making a head, there are 0.3mm extruders complete on eBay for less than £50.

there does seem to be a way forwards with mach3 as there are several bolt on type builders using their large CNC routers for 3d work just by slapping the extruder next to the router.

there is some slicing software "kiss slicer" that seems to have a direct connection to mach3 via its code creation so maybe it can be done easily, I really don't want to get into arduino et al just yet.

keeping on with the research...