Xclam is right about why the O.S.46LA will not fit. Their is just a tade if differances between the two engines. Now I think you could just change the engine mount to an adjustable style mount and you would be fine and all the bolt holes would match up for you. If you do not want to do that than I would put the OS46AX in it myself if it will fit without any mods.

Of course Stang stated above that the OS46AX is the same case as the OS46LA so that would not work for you if that is right, I have no idea myself.