The Avistar was designed around the OS LA 40 which has less displacement and therefore lighter than the .46 but it is also lighter by virtue of having bushings instead of bearings. The LA 40 is plenty of power for this plane so the .46 will be almost too much. You will have to add weight to the tail so that the plane balances correctly. Once properly balanced it should fly fine even with the .46 although it may land a bit faster because of the extra weight.