The Black Max is a great motor for the 20 from a power/weight standpoint. Have you checked out Luisp305's threads like this one?
http://www.classicseacraft.com/commu...ad.php?t=24110 Your 225 might not be quite as heavy as that 250 Yami but you could be in a similar situation. Should be a fun ride in flat water, but if you get into a short steep chop, you might wish you had less weight on the stern!