Vintage Machinery has a parts manual to wht I think is the 1-B (though I'm not sure from your description if this is what you have?):
http://vintagemachinery.org/pubs/2097/15219.pdf
Powerfeed motor (pg 74/75) just says part # is: 152543
PART #140 on that same page lists some motor options, one of which is Fairbanks Morse 3-phase. I see THIS motor on ebay which looks like it might be the right one from the VERY limited info I have:
https://www.ebay.com/itm/154343167850
The other is a Standard Electric 3 phase, but a quick google didn't bring that up.
BUT the picture shows that it just is a face-bolt motor, so perhaps that is something you could trivially measure and find on the market (OR, build an adapter plate for something else).
Page 28 and 29 show where the motor attached to the head, and it just specifies that there is an adapter plate for another face-mount motor, and the motor specs as:
150733 108 to 2825 RPM, 3/ 4 H. P . , 900 RPM .
143277 140 to 3800 RPM , 1 H.P., 1200 RPM .
143205 215 to 5650 RPM, 1 H.P., 1800 RPM
SO that one should be pretty easy to find as well; just come up with a ~1800 RPM ~ HP face-mount AC motor, and make an adapter plate.