You'd be doing well to find the older style motors/equipment unless you can find some old stock. A lot of companies dont update there sites often enough.
Everything has changed to meet your EPA standards so its almost impossible to find an older pre EPA effected machine.
Shindaiwa are pretty much on the nose these days with contractors since the Echo buy out.
I'd suggest just finding a good machine from a reputable local dealer.
That said, give me the link to the machines youve found.