Armed with fresh information from Sonex Tech Support, I set out tonight to grind the aluminum angles supporting the motor mount. This involved grinding more of the lower angle flange off of SNX-f15-02, the angles to which the mount fastens. This took about 3-4 tries to get it just right; removed high spots, etc. I like the resulting fit. As per Kerry at Sonex, if I get it within 1/8" of the specs from the drawing, it's OK. I'm not dead-on the specs, but closer to only 1/16" out, so I think that's fairly good.