Do you have any data or facts that verify the RS4's piston length and stroke match that of ours? Then, I would assume you need the Low Pressure Sensor swapped. And there's the fitment onto the timing chain cover.
I agree, I would also opt for an internal upgrade for the original. So long as its pressure regulator on top is in good condition, it comes with a new piston collar nut, and the piston end cap is not worn.