It turned out to be a much bigger job than I expected installing the stiffener between the inboard engine mounts. First I drilled the lower engine mount holes by stepping up through several drill sizes and using a 3/8" stainless bushing drilled out as I went. Then I trimmed and polished the angle for the inside, but put the two inboard holes too close to the edge of the longeron brackets, so I made a new one. Drilling these from the inside out was a tight squeeze for my fat body. I had hoped to have enough room to debur the holes without removing the engine mount, but no. So I primed both the upper and lower braces and set about other tasks.