Well, I see where you are going with the crank, but you would need to install longer crankpins for where they go into your center crank "joiner". The crank "joiner" would be a tricky piece to make, and the crank pins would have to be a precise press fit into the joiner. Then you would need a two piece crankcase that splits down the middle for assembly. No need to make up custom "clam shell" rods, you just put the rods in place on the crank before it is all pressed together. If it were me, I would then also pin those pressed joints.

It just seems a lot easier to use an Echo or Stihl or some other engine that uses a non-cantilever crankshaft to begin with.

Nice drawings by the way...

AV8TOR