Kochj
I am using the older OS 1.20 Gemini twin, which IIRC is exactly the same size as the 1.60. I had a friend make me some aluminum stand-offs and the engine bolted up perfectly. I put more effort into the fuel tank, which is way too high in the stock location, considering that these engines do not use muffler pressure and the carb is under the cylinders. I cut the inside of the fuse until a Sullivan 24 oz. tank would fit as low as possible. I still had issues with the mixture changing too much during the flight until I realized I didn't need that much fuel anyway. Now I fill the tank and then pump out fuel for 5 seconds and however much fuel is left in the tank is plenty for a 12 minute flight. YMMV literally
In any case, the only cuts to the cowl are for the needle valve and air-bleed screw (I have on-board glow), and a small square section at the bottom where the two exhaust pipe extensions exit. The sound of the twin is amazing!
SandyT