Hi Alan,
Here is my best attempt at a schematic from the lower buss board, through to the 651, following the S5E quad bus.
There are no resistors inserted or bridged along the route. There are some of the mods on each channel though. A bit of a mix and match of old brown, mod brown, and mod black modules.
It looks like for the bulk of it, that it is still set up as unbalanced for the most of it, and might be easier to go down that path. This console being only 32 channels, I thought i read (thanks for the links) that the balanced option helps the noise floor on larger consoles where it is more susceptible (?)
Michael at AES advised that there is documentation, but in Japanese. Luckily I have a long term friend who's job is to translate technical documents from Japanese. What luck.
Schematic from 82E19 lower bus card to 651 / 26 card
Underside of S5E connector on 82E19 lower bus card
Top view of both upper and lower bus cards
Typical "black" channel with resistor mods