Enco? Mill/Drill conversion

I am thinking about building a small CNC machine based on the Enco
Mill/Drill like Jeff Davis had built. (Cool web Site:
http://www.homecnc.info/cnc-main.html ) Has anyone else converted an
Enco to CNC? If so, what benefits or Red flags
did you come across in your adventure? I would like to retain manual
control of all three axis's when not in CNC mode, but
maintain a high degree of accuracy. The Z-axis is in need of a
creative solution. What about RongFu?

Thanks in advance for any ideas you wish to share.
Pete