In any case, I was successful in using the dividing head for the first time. I used it to put 36 flutes around a 2" (50.8 mm) cylinder. My calculations for rotations was correct at 40/36 = 1 4/36 = 1 2/18 holes. One whole turn plus 2 holes on the 18 hole plate.
I used the edge of the end mill to cut the flutes effectively making it a 45 degree cut. That was the tricky part--figuring out the location correctly. A little geometry and trig and I got it.
Yes it is a 1-1/2"-8 thread which is a common thread for many older 9" and 10" lathes. It might be tight since it hasn't been off, but it should just unscrew.
Handy as you can easily find other types of chucks with this thread if you want to use a different size chuck, a 4 jaw chuck, collet chucks etc. Once you get the chuck off the spindle bore has an MT2 taper so it can take a center or other MT2 accessory. This was one of the reasons I went with the PM dividing head, because the 1-1/2"-8 / MT2 matches my lathe so I can share some tooling between them.