That thing is bonkers lol thanks for the pics! I guess you're going into business making hobs and reamers now
But it looks like the gearbox fits yours like the old ones did, another aspect of the design that didn't change a lot. There are a couple youtube vids of lathe relieving attachments operating, generally quite low spindle rpm- though I guess the # of lobes matters a lot.
The spindle nose on my (and your) 12" is the same as the 14" lathe going back into the mists of time. My 1st ATW was a circa 1912 14" High Duty- the 1936 tooling fit it just fine- the only difference was a nice radius where the shank meets the shoulder on the new machine's spindle, the older machine's spindle had a sharp corner there. By the time I got the newer machine I had turned a backplate for the older one, which assumed that sharp corner, so I had to do a bit of rework on the backplate so it would fit. That meant chucking the 10" 4-jaw chuck in the other 10" 4 jaw, wishing I had a jib crane over the machine the whole time lol.