Why does the engine manufacturer make the tabs on the so narrow? Why not make them a 1/4 inch wider and position the holes a little closer to the outside of the mount so we can get a good secure engine mount? Of all the engines I have mounted the holes are always about 1/8 inch from the inside edge of the mount. It seems to me the engine tabs could be wider and still fit on the mount nicely since there is nothing to hit on the outside of the mount.

Why does the engine manufacturer make the tabs on the engine so narrow? (correction)

Must have something to do with their manufacturing processes. I believe you're right but I think 1/4" on each mount would be a bit excessive. Maybe 3/32 or possibly 1/8. Still a good thought.

Its a factor of leverage on the metal at the point of the bolt. If you make the tab 2X as wide, you have to make the metal 1.3X to 2X (dependig on the quality of the metal in the casting...) as thick or the torque of the engine will snap the mounting lug right off.

You would be unhappy to add 10% to 25% to the weight of the crankcase.

It is also a matter of making the engines fit in small places.

A wideer mounting flange would require the nose of the arplane to be wider to accomodate the engine. Not a bg deal on this Triplane. (plenty of room there...) But on a plane such as the 4*40... you wouldn't have room for anything larger than a .25.