Yes it is babbit. How do we tell if it is a 10D or !0E Thanks Dave wa5eab is what you needed?It is probably off of a Babbit bearing 10D or 10E. Please post a front view photo. And confirm that the vertical distance between the notched front or rear surface of the casting that sits on the bed to the center line of the spindle is about 5-1/8".
No, think of it as sitting on the bed. What we need to confirm 10" is the height (vertical distance) between the top of the ways and the spindle C/L or axis.
On the 10D versus 10E question, assuming it is all original, it is not from a 10E, because the 10E is a stripped-down 10D. It has no back gears and no threading gears. To tell whether or not is is from a 10D, we need a front view photograph.
OK. It's a 10". Now how about a front view photo???
Atlas used several different headstock castings between 1935 and 1939. With only a left end view to go by, my best guess at present is that it came off of a 1936 10nn (where "nn" is the bed length). It does not match the November 1937 10" photo shown in Catalog No. 28, which I am pretty sure is a 10D because the next page shows the stripped down 10E.