Very ugly without the cowl. IMHO, the airplane appears to be designed for a cowl and does not look correct without one.

I purchased mine used. The original owner never flew it but did mount an OS Surpass 91 on it. I'm putting a Saito FA-100 on it and mounting it upside down. I'm told this is perfectly OK with this engine. I have the same engine on an Ultra Stick 60, mounted sideways, and that combination works like a dream.

I haven't check the CG yet but the previous owner mounted a little less than an oz of lead just behind and below the firewall. The OS weighs 23ozs with muffler. The Saito FA-100 weighs 20.8ozs with muffler -- I might have to add a little more or shift the battery as far forward as I can get it.

Your OS FX .91 weighs 24.3 ozs with muffler, which according to my calculations means you will be able to balance her perfectly without doing much of anything. That's a lot of engine horsepower for this airplane???