Been fairly busy recently with other obligations. As a result not a lot of progress has been made. What I HAVE managed is:

• Gotten the waveform generator and phase/amplitude detector soldered not breakout boards.
• Wired everything up on a breadboard with an Arduino clone to test things out.
• Gotten a basic heartbeat (sine wave) using a 16MHz clock generated by a CMOS Schmitt trigger chip driving the waveform generator - note not being controlled by Arduino at this point.
• Switched to a clock generator breakout from Adafruit so I could drive the waveform generator at 75MHz; thought this would give better results than the jury rigged crystal+CMOS chip.
• Struggled to get ANYTHING to work with this setup. Unable to get waveform generator to respond to Arduino or generate clean output.
• Realised that breadboarding circuits running at 75MHz is PROBABLY NOT going to be successful.

So there we are. I think I'll try dropping everything down to maybe 1MHz max and see how that goes. The breadboarding is largely to validate how things are wired up, although I had hoped to do some measurements too. Have to see on that. This being my first project involving high frequencies AND a significant analog signal portion, I knew there would always be a sizeable learning curve. As for when I'll have time, that's less clear.