I think I am going to have to just bite the bullet and purchase a phase noise test set of some type. I'll have all the stability test equipment I need shortly as I have another board coming. But I also have a Cs, about 10 Rb units and two GPSDOs so stability-wise I'm covered. But I wish there was a way to measure close-in phase noise, like from 0 to 10Khz (but out to 100Khz) within the HF spectrum for less than $500. Every time I look for a test set they are mucho $$$$.
Something like this, perhaps? http://www.wenzel.com/documents/measuringphasenoise.htm
The challenge with this and others is that you need a reference source VCO that is as good as or better than the DUT or OUT, ha. I've played with these as they are easy to wire up on a breadboard. Really easy to test 10Mhz as I have a bunch of decent, better than average, HP 10811's plus the one in my Cs beam for a reference. Then you just need two switch the PLL loop constants to test 1hz, 10, 1K, 10K, etc. and using an external sound card adapter, you can get out to 100k using Spectrum Lab.
There is another version that uses a Johnson counter or quadrature hybrid (twisted wire quad hybrid by Breed et al, if IIRC) and then you get the I/Q advantages and you only need the source. Now that one I haven't wired up but was thinking about it lately.
I guess what I'm looking for is some type of external board, already put together with high quality, high-speed ADCs, all the transformers and mixers architected like the one you suggested or the one I mentioned, for less than $500. I can put it all together but the drawings are way over simplified because you should condition the input (those circuits are available) and I don't know if you need zero crossing for this or not.
Thanks