Corby - thanks for that. I checked the EFC+ and EFC- leads and they were correct. The problem was the position of the phase splitting pot.
I had it set for beautiful split, at inverted phase. After winding it around to the correct polarity (at the end stop), UNIT ACHIEVES LOCK!
I have three things remaining really to sort out:
1) Neg 20 rail is at -19.7 when positive rail is exactly at +20. This only when A7 installed. When I disconnect A7 power, neg rail returns to -20 exactly. I have a concern something is still amiss in there.
I expect the supply rails should track perfectly under good operating conditions, is that presumption incorrect?
2) Phase splitting pot range winds out. I can't quite get to good splitting even after tweaking all of the drive and match pots/caps on A3. I'd really like to re-center the phasing range on A8 from the edge of the dial - is this an aging effect maybe from dried out caps on A8? Has anyone looked into this?
3) The unit came with a 10811-60109 OCXO. When the unit is set to open-loop, the BNC control signal reads around 300 mV when tuned to on-frequency. Control drops to zero when I disconnect the 10811 EFC- SMB. When I swap out the 10811 for a 00105-6013, control is 0 V as expected. It appears I have an issue with the EFC- pin on the 10811? Has anyone seen this happen with units with a retrofit 10811?
Gents - thanks for all the help getting this far!