Waste is correct in that the motor that is different between a one and two speed pump. A two speed pump has 4-poles vs 2-poles so that you can halve the RPMs.

Also, pumps have an impeller which is matched to the horse power of the motor. So when replacing the motor, you need to match the braking HP of the old motor with the braking HP of the new motor as close as possible otherwise you either overdrive or underdrive the motor. Underdriving the motor will waste electricity and overdriving may damage the motor.

So if you can get the part number for the 1 HP Northstar two speed motor and impeller, you could replace both and have basically the same pump. The impeller may be the same as the one speed model but I would check that.