G'day Dave, A beast you say. A little on teh small size for my liking but it will do. I had wanted to get the next size up 13"swing with a gap and 24"long but I just don't have the room. The 1216 is the largest I can fit in my garage and still get the car in, with no room to expand.
So the answer is to build a vertical spindle milling attachment that will clamp to the bed after removing the chuck, and replacing it with a 6" pulley and a belt drive to the spindle then I'll have all 12 speeds available from the headstock gearbox.
A bit disappointing that the cross slide doesn't have "T"slots, and it's not really thick enough to risk cutting them. So my plan is to bolt a 1/2 "thick plate to the top of the cross slide with countersunk socket head cap bolts and have the plate predrilled with a series of drilled and tapped 12mm holes in a grid, this should allow me to bolt anything down that I need to.