No difference. if you find a difference, it would be in the size of the flex plate (for the smaller, higher stall convertor) or an internal difference for an HP motor opposed to a regular duty. The only other differences I can think of would be in the plastic gear ratio for the speedometer drive, and perhaps the arms to shift and passing gear actuation. All of those are easily changed.

If you have a different sized flex plate on your motor, use it, unless your new tranny comes with the smaller one and the torque convertor. Change the above things to the new tranny, and you will feel like you have what you had