You can pretty much mod any radio in the CB world by simply checking the filter bandwidths, and also adding value to the coupling capacitors throughout the audio chain and using some tantalum and higher quality capacitors replacing the electrolytics that often "pinch" the AF response. With an RF signal generator, (with AF generator built in) and a scope you can sweep the chain for response and rolloff. You can widen the sections up, to a point within relation to the filters. Also in some radios the RF bypass capacitors can pinch things a bit too, I have seen people try to "broadband" a radio and forget this step. It's no magical science, just a bit of basic electroinc knowledge.