1. will this work?
2. is there a better way?
3. how would you do it?
4. can this be done PIC to PIC without the decoder
If I smell what you're cooking here...
1- It might, won't know 'till you try it...of course it'll be too late then
2/3- If it was me, I'd use the FFT on the Rx end, but that would cost a licensing fee, so a '567 might not be too bad an idea.
4- If you can get a clean enough audio output, COUNT may be able to pick up the FREQOUT'd audio and you could COUNT the audio coming across watching for the right frequency. The book says PBP will COUNT up to 25Khz at 4Mhz oscillator.