Rather than mess around with shims to get my lathe tooling centered to the chuck, and to enable me to use boring bars and parting tools, I purchased a Phase II+ quick change tool post from Enco. After reading a significant amount of information on how to get this piece to fit on the 9x20 lathe, I was a little apprehensive. However, after about two hours of shop time it is mounted and works great!
The first thing I learned is that making an adapter to get the new QCTP to work with the stock tool post stud is easier than I thought. I simply took the stud that came with the new post, cut off all but about 0.75" of material below the threads on one end, then drilled and tapped it for M8x1.25. That enabled me to screw that adapter onto the stock stud, slip the new tool post over it and use the included nut to sinch it down. Much easier than I thought it would be!
The other thing I learned is that 1/2" tooling seems to work fine for me without modifying the compound slide. I had read elsewhere that this modification was necessary, however I've got the tool centered and everything seems to work fine. Perhaps I'm missing something, but if so, I'll likely discover it in the future and, at which point, I'll post my mistake here! :-)