-- Last Updated: Feb-14-13 7:00 AM EST --
That gives you instant access and you can easily operate it with one hand (either one). Both of these can be important factors if you end up in a situation where you really NEED your radio. In your case, it will also allow you to select any PFD you want.
It's pretty easy to do with most radios, using the standard belt mount block that comes with them (the type that uses a post/button on the back of the radio and requires you to invert it to release it). Attach the mount to the shoulder strap along with a loop of bungee cord that fit's snugly around the radio to keep it from inverting. A short leash from the radio to the shoulder strap will prevent it from getting lost if it does manage to come out of the mount.