I was looking at a photo of this radio. http://www.jk1mly.org/radio/catalog/kdk/kdk-fm2016.jpg
If it were me, I would consider installing and wiring the internal pot control to the external RIT selector on the front of the radio.
Replace the RIT selector with an internal potentiometer control and since this is an FM only radio, you can set the RIT control permanently inside the radio.
OR here's my favorite,
Replace the current RIT control with a "pull out" style dual potentiometer.
When pulled out, it would function as a tone control and when pushed in - an RIT control.
PL tuning would be accomplished by selecting a marked increment on the external RIT selector.
This would provide more precise tuning that is used to generate a particular PL tone.
Charles - KC8VWM