Hi Rysiu,
Cutting the brace not your only option, but if you did the web in back of the coil support should give the need rigidity. Another idea is to reverse the cylinder putting the muffler on the oposite side. Also the piston would be reversed so the pinned ring would retain its orientation. The Cylinder will bolt up fine. The big issue with this idea is making that the transfer ports in the crankcase are not blocked and removing any material so the ports are a close match. I tried this on my 18cc featherlite, but didn't do it because the lower rear transfer was molded into the back plate. I am looking at my 25cc weedeater blower motor now and it will work fine with it. It would have no blockage tranfer port blockage. I would remove the center web in the top of the crankcase, because it is going the wrong way with the cylinder reversed. See my pictures below. Another bonus is that the hot exhust side of the cylinder will now be exposed to prop blast for better cooling. I didn't have to cut anyting on my 25cc to reverse the cylinder. Just remove the back plate. unbolt the cylinder. With the piston at the bottom of the stroke slip the con rod off of the crank pin and reverse the cylinder, being careful not to dislodge the piston from the cylinder. Slip the con rod over the crank pin and bolt down the cylinder. Check to insure that the transfer ports are unobstructed and the engine turns over freely. Replace the back plate. Slight trimming of the cil support wab may be required. Of course I am not resonsible for any problems that may ocurre since I am not performing the proceedure. Either way the larger muffler is better. Good luck.

Dave