I am sure you will find opinions both ways. I have a 66' step pulley J head I am restoring and converting to CNC. I decided to do my own conversion after looking at what others have done. Sort of followed what Vince did on his conversion. Search the forum for user Vince (N4NV). Also Ray L. (HimyKabibble) did a very nice job on his BP clone conversion. There is lots of good help around here.
Started my conversion several years ago, built the motor mounts but then decided to restore the tired mill before spent more money on CNC parts. Stripped it down, had the ways ground/scraped, installed some new bearings and put on fresh coat of urethane paint. Started out thinking I could use the acme lead screws for a while but I could only get the backlash down to about 5 thou. Then I got a lead on some ground ball screws which I just got installed last week. Should have the X and Y steppers installed in the next couple of days then its on to making the knee drive stepper mount. A quill drive is in the works for early next month. I didn't do a thread of my conversion but pictures area on line at http://picasaweb.google.com/cschaffter/CNCMillProject#