I mounted an OS 1.60 twin in mine. Fits perfectly, is a very good match power-wise, and sounds great too. There's about 1/2" clearance between the cylinder heads and the side of the cowl. I only had to cut about a 1/2" notch out of the center rear trailing edge of the cowl to let my 2 brass tube exhaust extenders slip out below the cowl bowl. Because the 1.60 has a very short integral motor mount, I did have to build a ply box to push the engine forward an inch or so. I also built a semi (very semi) scale tail wheel from brass and a Dubro 1 1/2" tail wheel. If you plan to mount an after market tail wheel, be aware that the balsa towards the tail post is not very thick or hard. My tail wheel screws pulled loose after a dozen flights or so. I ended up cuttting out a 2 inch length of balsa out to the side stringers, epoxied a 1/8 ply plate to the stringers and then filled the hole with fairly hard balsa.

Also, a little cockpit coaming really dresses up the cockpit openings.