Industrial Motor Soft Start Application

Hello,
I have an older Westinghouse Motor that the ancient soft-start went bad in.

I want to put an AB soft-start on it for slow ramp up. Although there is a bank of resistors ontop of the control panel we just let it coast to a stop (big flywheel effect). Here is what I am confused on. Our maintenance guy says he just changed the brushes, I thought AC did not have these? Also does any derating need done when the RPM on the name plate is only 584? Here is some nameplate info if it helps.
Do you size for FLA or Rotor Amps? I have dealt in 25HP and less and this one scares me. The owner said he paid 25K to have this rebuilt....................is that possible? Is this special? I know the RPM is not standard but what does that do for sizing a soft-start if anything. I have had several opinions and would like to hear from some of you.

thanks so much in advance!
Randy
Westinghouse
Induction Motor

Type CW
60 Cycles

Inst Book 7099

Ser 2519P42

32B Frame

253 AMPS

200HP

Rotor Volts 236

Rotor Amps 384