Any eddy current tester designers out there?

I have experience with analog and RF design but none with eddy current testers, and I need to design a front end for a ***** tester like the MIZ-23 or MIZ-27. I've studied patents and prior art a little, and have a reasonable idea of what's required. The usual approach is to differentially measure probe coils while the transmit driver operates CW, cancel the remaining drive signal from the received signal using a balancing circuit, and then do a direct quadrature conversion to baseband. Movement of the resulting baseband vector then represents flaws in the material being tested.

What I would like to know is a little more quantitative information. What are the characteristics of the typical flaw signal? Amplitude, phase shift from the carrier, etc? How important is phase noise on the tx? What noise factor does the rx need? Anything particular I should watch out for?

Thanks for any help!