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Sure why not just match the head height with the height of your output and that will give you your gph. Make sure you don't exceed your overflow rate when choosing a pump.
If you aren't sure of what your overflow is here is a chart to help You can always do the test yourself to know for sure.
Match up as close to your overflow speed as you can and be sure to put a ball valve on the output of your pump so you can slow the flow down if needed.