This would also go for drilling slightly undersized and using sheet-metal screws. Another no-no.
And yet both TopFlite and Great Planes (same company now?) instruct this as the method of attachment in at least three kits of theirs: Easy Sport 40, Contender 60, Ultimate 40, and a handful of their ARFs (but that's no surprise as it means less hardware). I had a well campaigned Big Stik 40 with an OS FS70II screwed to the mount. The largest piece of the engine body was still screwed to the mount after a midair and lawn-dart into a rock.
May not be the best method, but as they said at the Mig Plant: "Perfection is the enemy of good enough."