I like the idea of using some of the old "brick outhouse" type radios. The
MasterII and Micor are about as bulletproof as a radio can get.
Another idea that I saw on the web is to use a couple of portable radios
(i.e. MT1000 or P200 Motorola) radios as the Receiver and the exciter and then
use a commercial PA of your choosing. If you add some of the mechanical folters
from an old Micor, you could have a programmable, multi-channel device for not
too much money. It will take a lot more time, than the modified mobile.
My $0.02 worth. Good luck. This could be a fun project.