Just take it to your local community college and have the top dawg aluminum tig welding student bevel both sides and weld it back on. I have done this many times, and since the crank case is cast aluminum it shouldn't distort very much or enough to hurt it. Make sure it is completely disassembled, in other words no seals or gaskets.

I am a career weldor, yes the puddle is dirty but if done right should hold well.
use 3/32 E5056 Aluminum filler rod. A/C, High frequency
Tungsten: PURE (not thoriated or anything else oriated) or rare earth only.
Start out with 35 AMPS
GOOD LUCK
PS-I made these mufflers for my AIR HOBBIES (Sachs-Dolmar) 50cc twin as the stock ones I felt were too heavy thereby lightening it by 9 ounces.