The original Legend, Legend Cx, and Legend HCX all use the same handlebar mount - I have had them all. But the backplate of the original is different than the cx and hcx, the latter two use a little clip that screws onto the back of the unit that allows it to connect to the handlebar mount. These are hard to find, but a call to Garmin will get you set up quickly. Call don't email, the results are vastly different.
The newer etrex 10/20/30 units use a different mount system. I made an adapter. :-) I mounted the clip from an hcx onto a belt clip for an etrex 30, now my new GPS fits all my old mounts.