That old school 2 stroke nissan is way better of a engine compared the a etec. You should be able to get mid to high 20's with it on that boat. Keep in mind a good prop with added cup for a tunnel has alot to do with the overall performance. Also,motor height is very important as well. Tunnels can be a pain to setup,but once you get it it right leave it alone. I would use a powertech sra 3 blade 11 pitch and have a propeller shop add the tunnel cup.
http://www.ptprop.com/component/page...art/Itemid,46/