One thing that I forgot to mention is that Timken bearings have the advantage that if you or the PO wear or wore them out, replacing them is easily doable. Whereas replacing damaged babbit bearings isn't easy.
However, if both types are in good condition and properly adjusted, you can't tell from the finished part which type of bearings were in the lathe that made it. So if your bearings are in good condition, run it. In the home shop, the lathe will likely outlive you.
Also, download the Technical Bulletin on the Atlas 10" and early 12" headstock. Although the spindle covered is Timken, the back gears in all of the ten Craftsman models that had them are the same. And the TB covers them.
Robert D.