There are 2 standard mounting dimensions. One is the width or lateral distance between the center of the holes (dim A) and the length or longitudinal distance between the centers (dim B). Most manufacturers publish this stuff (especially OSfor all current and discontinued engines). Dim A for both engines is 1.59 in. and Dim B for both is .69 in. Ijust hate it when they use standard measurements rather than metric! In metric it's A - 44 mm, B - 18 mm.

www.osengines.com/engines/engine-specs-discontinued.html is the OSspec page with all this stuff.