I have updated the schematic for PDH box #1437 (primary loop) and put it in the gyro wiki. I have not been able to take a new transfer function with the Agilent, as it seems to be too noisy for some reason. I will use the SR785 (which has a higher input range) to make one ASAP. In the meantime, the general shape can be found in ELOG 1080 (this TF would be fine but the gain setting was not recorded at the time).
I also measured the change in gain as a function of the dial setting, which is linear in dB (as it should be given the specifications of the AD8336 variable gain stage it is connected to). I did this by injecting a sine wave @ 1kHz with the FG and measuring the amplitude at the output. For some reason, the results I got seemed unreasonably high (~112 dB with G = 0.5, whereas the TF linked above shows ~40 dB @ 1kHz, which would be unattainable for any gain setting given my measurement). It is possible that I was driving with a higher amplitude than I thought; I will repeat the measurement tomorrow).
Finally, I verified that there is a factor of ~40 gain from the INPUT to INPUT_MON ports on the PDH box, as seen below.