One thing to remember about CTCSS is that the tone frequency has to be pretty close, like +-1% or so. If your tone is supposed to be 100Hz, and your encoder has drifted to 102Hz, it probably won't work. Drift on free running oscillators is going to be a problem, unless you use very tight specs on the caps, and keep the thing at a fairly constant temperature. Normal caps will easily drift 5% over a 20 degree temperature change, so as the unit warms up, it might require continuous adjustment.
Your best bet is to get a commercial unit, some are very small. I had one years ago that readily fit in an Icom 2AT, there should be no problem finding one for the larger radio.
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