a major differance with the boats designed for the self tacking jib arrangement is that the forward beam has been positioned significantly forward and therefore percentage of jib size compared to mainsail size can be reduced. this also affects the spinnaker head location to provide for a well balanced boat under all points of sail. reducing the size of your jib on a h20 will take away some of its design balance. and the spin head attach point will be farther aft than ideal. thats my take anyway. good luck