The Kollmorgen CTI-187-2 motor has a 24 Volt speed controller that is located inside of the motor. So to be able to use an external speed controller with that motor it would need to be taken apart and the wires going to the internal speed controller ran outside of the motor.
The CTI-187-2 motor is fairly fragile when running on 24 Volts so running it on 48 Volts could be very stressful for it. It might work if there was a very small load on the motor such as if it was being used for a non-vehicular low demand purpose. I just can not see it holding up for very long if used on a vehicle and ran with 48 Volts though.
We have never run the wires outside of the motor so unfortunately, we can not offer any advice regarding how to do that or which wires to connect to a modern BLDC controller. The wires may have universal colors though which would make connecting easy. Also not sure what 48V BLDC controller to recommend for it. A 500 Watt controller would be easiest on the motor, however, may not provide much more power than the original 400 Watt built-in controller. Just about any throttle can be used with a BLDC controller as long as it is a hall effect throttle.