Here are the whole information about Aero .35 : http://www.modelenginenews.org/cardfile/aero35.html

Really the engine are heavier and longer engine than common model engines in same engine size, the plane need tailheavy to have the Aero .35 to get right C.O.G. (balance)..

RCV engine are more compact in length since the sleeve are used as rotating part to drive the propeller. Do not affect so much in C.O.G. in the plane compared with other engines in same plane.