Did he (LHS guy) talk you into the Evo because it's what he had on the shelf? It ought to to be enough power, for sure. Side mounting the two stroke is probably your best option, a fair compromise between aesthetics and reliable running. Mount it with the cylinder to the right.

I'm curious to know what the LHS guy said to convince you to go 2-stroke. They may take a little more work to set up well, but it's worth the work, and not difficult. You may have to try a different engine mount to get it (the Evo) to fit. My inverted .65 in my Sig came close to the top of the firewall, but the engine is almost totally enclosed within the cowl. I used a DuBro antivibe mount. On my H-9 Cub I used a Dave Brown mount, and I recommend it highly. The part that goes against the firewall is round, and has marks you line up on the crossmarks that you make on the firewall to center your engine, makes it easy to center everything.