I just found this thread and am reading with fascination: I'd love to find a JMBB some day. My daily driver is another of your designs; a Paragon System E. I've had it since the late 1970s and other than building a new PS because the old stopped functioning, it's pretty much as I found it. I think it was modified by a previous owner. The volume control is a stepped-switch, matched-resistor type. Also, were all the signal path caps bypassed with polystyrene originally?
Anyway, I thought @RealMarkDeneen might enjoy knowing at least one of these is still out here making music.