I bought my 7210 used and the monitor was already in it.  There is an OEM part available that is basically a rod with eyes formed on each end that bolts to the FR cab post.  You then use clamps to attach the monitor, etc to it.  {I deleted the photo originally with this post.  See the photos below for more details inside the cab.}

As for the radio, I mounted my VHF rig right in front of the shifter.  Most of the Magnums I have seen have had the sun visor removed in a fit of frustration, and I thought about mounting it there.  But it looked like more effort than I wanted to go to.

One thing to consider is the effect of the radio on the electronics. In my off-farm work I sometimes drive a propane truck.  I mounted a 45 watt VHF amateur radio on the meter computer with custom bracket and a ratchet strap and a mirror mount antenna.  Another guy did a very similar thing with his 4 watt CB.  I had no trouble with my radio, but every time he keyed up it locked up his meter computer.  Needless to say, the boss was not pleased.  I know if I transmit with my business radio when planting the population monitor goes nuts.

Where do you plan on putting your antenna?  On Dad's Magnum he brazed a flat piece of metal to the right mirror bracket and mounted an antenna there.  On mine I ran the coax along the monitor leads through the cutout on the lower rear window.  I had a piece of galvanized sheet metal I got someplace that looked like a channel iron with flanges on each side.  I mounted my antenna on it, ran the coax under the channel, and used about 8 sheet metal screws to attach it to the fender at the right rear of the cab. You can just see the tip of it in the photo.  It isn't at good as Dad's from a signal propogation standpoint, but it is adequate for our use and the antenna is better protected from being beaten around.