No, the radio doesn't get down into CB freqs. I couldn't justify keeping the CB mounted permanently, the only people in this area that are on 11m are running illegal rigs, splattering their signal all over the place. It's a nightmare. On the rare occasion that I want to be on CB (like for the trails) I have a Midland 75-822 handheld. I kept the same antenna mount (3/8x24) on the Jeep, so I can swap the antenna cable from the 2m to the Midland and swap out the antenna with the CB antenna, and I'm good to go.
I like the RR mount, especially considering no drilling or modification of the Jeep is needed. The Cobra 29 radio mount will need to have a screw hole drilled in the center to work with the RR mount because the existing holes are too wide apart to match up. There is, as expected, a bit of an issue with bounce on the 2m radio. Crucially though, I don't expect that it would be an issue with a full-size CB like the Cobra 29.
See the attached image.
[Edit: aaaannnnndd it's upside down when inserted. Nice. Sorry about that] I know it's not great, but you should see two velcro squares on the top, back corners of the radio. The matching halves of those were on the plastic header cover in my previous installation. When I hold the Cobra up to the RR mount in the correct position, it looks to me like those back corners
will reach the header just like it did before.
This means that the radio has
four solid contact points: the two screws on the sides holding the Cobra to the mount, and the two heavy-duty velcro tabs on the back corners. In my previous installation, bounce was negligible. With the new mount (although I haven't actually mounted the Cobra to it, so take it with a grain of salt) I would expect it to be at least as stable, quite probably even more so.
Sadly, since the 2m rig is smaller than the Cobra, is just barely doesn't reach the header, so the velcro option is out for me. I haven't bumped it around yet to see how it holds up -- if it's a problem, I may need to devise some other solution.