Which Ryobi is the copy of the Gz400? Seems like a lot of different saws are coming up on CL lately, and if one of these can be made into a hot little saw /cheap/ I am all for it.
Model 10532.
Amazon.com: Factory Reconditioned Ryobi ZRRY10532 18-Inch 40cc 2-Cycle Gas-Powered Chain Saw: Patio, Lawn & Garden
There's also a Craftsman GZ400 and a Craftsman Pro GZ4000.