I have the same boat(74 23'Tsunami) with the 5.7 liter I/O.
I went with Bennetts drop fin tabs.I know this sounds crazy but I can't remember the exact size,but I'm pretty sure they are 12x12 drop fins.
Call Tom or one of the guys at Bennett,they are incredibly nice to deal with.They'll set you up with the right size tab.
They actually recommended using two sets of tabs for my Tsunami,but told me if not,then to go with the drop fin tabs.
They explained that the drop fin adds a lot more lift effectively acting as a much larger tab,and they also help make the boat track straighter.
They were right,as these tabs do a great job.
Don't confuse the drop fins with the sport tabs.The drop fins have a much larger size drop fin.(about a 3" drop)I don't see the drop fins on their website,but I know they have them.
I placed mine on the outside steps of the hull,and they do a perfect job of controlling the boats attitude.I don't really have to use them all that much to get on plane,as the boat hops right up pretty quick.I use them more in a quartering sea more than anything
Here's a pic of the tabs on my transom in the early stages of the restoration.I had just mounted them.
