You might get a fairly good handle on the GPM required by the engine then size the filter accordingly.
I use a RACOR 690T (90 GPM, 10um), OEM is 45 GPM, 10um I think. I just 2x the OEM to be SURE I was not creating a restriction. RACOR because that is what they do best of any of the commercial companies - filter (my opinion obviously, flame wars not needed).
Bob Weis