While from a practical standpoint you are absolutely right, there may be another approach. You design the plane so that it could be built with two levels of structure. An example would be to design the plane for the larger engine but then modify the design/structure for a much lighter mission. True, the savings would really be dependent on the structural type and the materials used but it may be possible to design in some flexibility so that the two airplanes could be built with exactly the same tooling, just with lighter gauges and maybe a more limited mission profile (slower speed, less range, less payload, etc.). In this way the company has two nearly identical products and is able to hit two markets with much less investment.I dont think anyone could design a plane that would use either a IO390 or a 914; it would not be optimized for either. At some point the 914 will out perform in HP but it will never out perform in torque, not in practical flying. The 390 will turn a bigger prop with more pitch. The only 914 I know at my airport is in a wrecked 3/4 Storch, It is a good sized airplane and light. There is a IO-390 in the hangar next to it in a RV8A. No way the 914 would ever fly that RV unless you had 10,000 ft runway. In the summer, the density altitude at my airport can be 5000ft; still no way with the 390 handicapped. The 390 has made it the fastest RV at the field; he went from the slowest with an RV4 and 0-320. The 390s are now STCed for Mooney injected replacements. A Mooney 20E is almost 2600 gross takeoff stock. There is a Pulsar with a 912 an airport over, cool little plane; way smaller than the RV; about the same speed.