If you post a close up photo of your pump then might be able to get the pump curves but as pointed out above it will only pump the same volumes of water at a much lower head than the UPS3 so far less need for balancing/tweeking lockshield valves if UPS3 installed.I have checked with the grundfos replace app and it has highlighted the ups3 as a direct replacement for my existing grundfos 15-50x18. if the outputs are matched wouldn't I still have the same problem?
The UPS3 is a direct replacement but you would have to choose different pump curves to give the lower head that your pump is pumping presumably on speed 3?.