I have an Arco "Roto-phase" from the 1970's, 1 HP rated. Frame 56 motor, modified.
The innards are pretty boring, one 40 uF start/balance capacitor connected to the 3rd line.
Contactor is external, an older Furnas.
It works fine, although it was a little noisy until I re-balanced the rotor, and used some silicone on the sheet metal box containing the capacitor (attached to the motor frame). Looked like a balance weight had come off some time ago.
Added note: this one pops right up to speed, no delay.
The rotor is quite different from a motor rotor, yes. I didn't take any pics while I had it apart, but it had IIRC, more rotor bars than normal, and they were quite a bit thinner also, but made of copper. SO I don't know the general rotor resistance.
Higher resistance rotors would not have as much phase lag inducing rotor current, which would have an effect on generation and starting.