My 4*40 ballanced right with a Magnum .44 gp (bushing bearing) and the battery right on the CG. I changed to a Magnum .40 XL (ball bearing.. heavier) and had to put the battery behind the TE of the wing.

The O.S. LA.46 is lighter than the Magnum .44. Not sure how close the .40 LA is in weight to the .46. Might just try a brass "safety" prop nut (and watch it need the battery to be behind the TE of the wing...)

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Note... all the above engines fit the same bolt holes.