Nice work!! I think it's going to be a sweet little engine!

Looks like the crank snout left sticking out after adding the third bearing is pretty short??

What size carb are you using?

Yeah, any shots of the crank put together?

Here's a pic of a muffler I made for my 23.6cc Echo in my Fokker. It's a steel tube, squashed oval, with two end caps brazed on and two outlet tubes in one end. I also brazed in two tubes for the mounting bolts to go through and tighten up without squashing the muffler. Works great and sounds good! A variation might work well on this twin...

Thanks, and congrats,
AV8TOR