I thought most engines had a "rating" of how much fuel they would burn at wot and or cruising speed. I have not been able to find any info of the sort on my boat. If this helps I have a 19' Bayliner Capri 1952 cuddy
I have a 2000 1952 with the same engine. I can't be of any help right now, but last night I installed a Lowrance fuel flow sensor, and should be able to post some numbers in the next few weeks.