Hi,
I'm not too much of a specialist in SYSTEM-11, but I've already worked on a #High Speed and the function of these additional boards with capacitors intrigued me!

☛ The schematics can be found on IPDB here :
https://www.ipdb.org/files/1176/Williams_1986_High_Speed_Instruction_Manual.pdf.

☛ Important, don't miss the amendments :
https://www.ipdb.org/files/1176/Williams_1986_High_Speed_Amendments_and_Additions_to_the_Instruction_Manual_probable_date_Apr_2_1986.pdf

Indeed, if you look at the original documentation, the additional boards are not mentionned. You will only notice two left/right hideout relays :
schema (resized).jpg

The key is in the amendments : there is a modification to the schematic, and two boards with resistor/capacitor/diode has been added.
And here, you will find the values of the components:
➤ Resistor is a 150 Ω 1/2 W
➤ Capacitor is a 100 µF 100V
➤ Diode is a 1N4003
➤ The diode mounted on the relay is a 1N4001
board (resized).jpg

As far as I understand, they replace the original "black" relays by another model, and add the capacitors/resistor/diode, probably to increase the hold time.
The two B-11160 boards are located near the relays:
relay1 (resized).jpgrelay2 (resized).jpg

The resistor got hot, but the capacitor is also old and probably "dry" (normal, after more than 35 years). My recommendation is not to hesitate to replace everything, the resistor, the capacitor and at the same time the 1N4003 diode.