Dan Healy is selling it, the guy who modded most of Jerry's rig. It does not have the 90's rack mod because it was not the one used in his live rig, at least post aug 79.
Closing of Winterland new yeara eve 78 shows the gray knob in use as well.
"The process of selecting the tone on the guitar is an aesthetic process like any other, so you try a lot of different things. Most of the things I’ve tried I’ve tried in live performances" ~ Jerry Garcia