I had an engine like the one in the third photo, but I gave it away. I don't remember what it came out of now. I also have an Echo 30cc that looks like yours, and I have one out of a chain saw that has the carb on the bottom with a reed valve like your "mystery motor". Haven't done anything with them yet, but they will make good conversions....

Bearings and seals are more universal than people realize. Engineers design around off the shelf, semi-standard size bearings and seals when possible. Try any good bearing warehouse and they will probably be able to match you up with what you need.

AV8TOR