That model and serial number is very likely late 1940s to very early 1950s. It's called a 12" model, but the swing is actually a bit over 13". I've never been sure if the T was for tapered bearings, or a factory installed taper attachment, but that one definitely has the taper....probably $500+ on eBay all by itself. I've been trying to find a taper for my 13" Sheldon for a while without luck. The E is for economy drive, so you get four speeds in direct drive and four in back gear, for a total of 8. Most have a low around 70rpm and a high of around 1350, but that could vary with model, vintage, etc. It looks pretty complete, and appears that it hasn't led a hard life....nothing obvious damaged or missing.
The thread indicating dial is there (just paid $75 for an original for mine), so that's a plus. If they have the steady rest or follow rest it would be a huge bonus...even more than a 4-jaw chuck since those are easy to find.
Someone made a spider for the end of the spindle, so they were almost certainly using it to chamber rifle barrels. Sheldon lathes were actually quite popular with gunsmiths back then....fairly heavy for their size, and a spindle bore large enough for most rifle barrels, while having a fairly compact headstock that would allow them to chamber barrels on the short side without having to run the barrel
Overall it looks pretty nice! There is a Sheldon Lathe IO group you may want to check out.
sheldonlathe