Clausing still sells a fair number of Atlas lathe parts, and a few mill parts. You will probably think that the prices are high, but they simply reflect typical prices for recently made parts made in USA and not China. And they are usually lower than any prices quoted by Sears.
Also, if Clausing no longer carries a part, they will usually email you a TIFF scan of the original drawing. We have a lot of those part drawings in Downloads, many of them cleaned up by me. But none that I can recall of the specific parts that you are looking for.
At any rate, the threaded bushing, flat washer and dial are the only parts that you need to make the conversion. The cross slide and compound lead screws, cranks, gears, keys, outside nuts, etc., remained the same. And it is possible that you might be able to convert the dial from early to late version. Clausing probably has the knurled thumb screw that locks the dial, as it was also used on the Atlas Mill.
I can definitely recommend the conversion to anyone with the early version of either the Atlas or Craftsman 1/2" bed 12".