There was one I posted in the link you refer to, This was on an Excello that the knee had been retrofitted for positioning only, Using a ball screw jack.
Personally I wouldn't use the knee for Z axis control.
It sounds like you are using belt drive? What ratio?
Old link here http://www.cnczone.com/forums/showth...ballscrew+jack (*Knee Mill Retrofit*)
Mine has a pneumatic cylinder either side of the knee for counter balance.