Sorry Terbobob,
Check your physics, thurst does best when running through the COG. Whether it is pulling or pushing, the most efficient use of thrust is through the COG. some exceptions do exist, especially when there are more than one force being placed on the craft. For a standard boat, the best setup is a mid engine with a straight driveshaft (the engine sitting on the COG) The same goes for airplanes (although the engine is not on the COG on most planes, it is in the same line of thrust). With Airboats, the engine aloft works because there is a counter force of the hull pushing into the water, similar to having a multi engine setup on an airplane(where the force is balanced between the engines). This is what leads to most blow-overs, when engine force is suddenly decreased, and the force on the hull takes over. http://image.rcuniverse.com/gallery/...humb-33413.jpg is my latest boat. take a look at the engine mount - yes, there is a nut under the front motor mount. the COG of this boat is about where the radio box meets the fuselage (and in line with the engine thrust) http://image.rcuniverse.com/gallery/...humb-33405.jpg is my first boat, pusher, clearly the AOA on the Cowling can be seen. Although the engine thrust misses the COG (where the 'nose'meets the 'struts' - under the chin) it is only by a couple of inches, and still worked very well. Neither boat has ever blown over, and the yellow boat has only rolled (sideways) on dry land.

Try this - take an airboat, if a puller, hang it from the propeller hub, and look and the angle she hangs. Is the thrust line (gravity)where she wants to go (where is the bow pointed?) Conversely, with a pusher, balance the boat onthe prop hub, is the thrust line the way the boat wants to go?(again, where is the bow pointed?) Again some offset is ok due to the counter force of the water, but try to get the thrust to go through the COG. Most other concerns are for the build - where to attach the ruddres, heat concerns for the pusher, and of course personal preference. Personal Opinion - the pushers will handle better, due to the distance (leverage) between the thrust point and the COG, but this is the reason the yellow boat has the tail it does, leverage for turns. At this point, I would have to agree with the Cajun Gator, the best way to know for sure, is to experiment (build and race).
Sean