Hello John --
I don't know if you prefer to reconstruct a historical AFSK design, or if you are simply looking for AFSK functionality (perhaps via a new design).
I'd be happy to do a layout of a modern AFSK oscillator board for you. I've been working with KiCad for about the last two years and am now pretty good at doing board layouts. I get boards from China, five boards for less than $6 total, delivered to my mailbox. The only hitch is that the boards can't be larger than 3.9" in either dimension in order to maintain the prototyping pricing. I haven't found that size limitation to be much of a problem. If the board layout does go over 3.9" the cost isn't a lot more, but it's enough to try to keep things to 3.9" or less.
I've also been doing a lot of work with the AVR-DB and AVR-DD series of microcontrollers ($1 to $4). To quickly boil it down I have a working design for a two-tone paging generator that implements an audio frequency (4 Khz or less) Direct Digital Synthesizer in software that outputs step-sine wave on the internal DAC. Any change in frequency (AFSK) is phase continuous thanks to the DDS. Also, because I use a crystal for the timebase of the AVR, the audio frequencies are accurate to about 1/100 Hz. To clean up the step-sine wave I follow the DAC output with an 8th order Butterworth low pass filter, which sounds like it would be complicated, but it's just one 14 pin quad op-amp package and a surround of 8 Rs and 8 Cs. The Rs are 1% and the Cs are 10%. If I only need low current AC output the last opamp can deliver several milliamps at 3vpp. If I need big current output then I follow the last filter opamp with an LM386 speaker driver, which is good for about 700+ mA at 3vpp.
If it was desired to really go fancy, a socket for a micro-SD card could be added, and the SD-card could hold PCM files of audio modem tones to be sent out the DAC. I haven't tested that with tones, but I have with human speech and it works pretty well with that.
Let me know if this, or something similar, might be of interest.
Paul, ad7i