I am making a set for converting the BF20 to CNC as well. I have finished my initial designs, have included some pictures of it. The kit will become available at www.damencnc.nl after testing is finished. The parts will be made from laser cut stainless steel plates. Covers are in the making so work can be done with coolant.
I had some question about your design, which is interesting:
Are you using the motors coupled directly to the axis? Don't you have problems with resolution? Even with microstepping, a direct connection often causes problems unless huge steppermotors are used.
I am using belts so that smaller motors can be used... Have runs mills like these with 1.5 to 2nm motors and they work great..