It is possible to install the FC347 or the FC390 frequency counter into this radio, below is a picture of the wiring hookup, please note that the RF connection's center conductor (shown at the top) should have a 68pF ceramic capacitor installed in series to help prevent loading of the CB's circuit.

Sonoma also mentioned that it is necessary to modify the frequency counter inside, this is a jumper that needs to be added, I have added the details for the FC347 and FC390 modification here.