RE: PCM 512 to 2.4 convesion
An Idea:
Get a spare 512 receiver and take out the decoder board. Run the 512 modulation in the transmitter through the decoder and produce the PWM outputs. Putting the outputs into a PWM frame is now trivial for a EE tinkerer. Hack a TM-8 module and you have FASST.
PCM 512 was extremely slow. This is the reason that I skipped it and waited for 1024. But only you know why you want to save this transmitter. A neat MicroStar conversion would make more sense and already mentioned above.