This is how you look up Echo equipment.

http://www.echo-usa.com/documentation.asp
It's a 21cc engine.

The engine it's self is a good engine. Other cylinders fit the the engine block.
The 23.6 cc engine is the best over all engine to build but this is a good one also.

Most echo engines are very good and have a following all their own.
There are a couple of companys the build RC engines using Echo as there base engine.

Prop hubs and other conversion parts are available on ebay as well as other companys on the internet.

What are you going to put it on?