Well, crap! I can't find it. So here goes from scratch:
The start of the grounding points is terminal 3. This jumps to the 2 left lugs of the volume pot and back from there to the RCA jacks. From the top left lug of the volume pot there is a grounding jumper to the two bottom lugs of the headphone jack. This jack may be different than what is being delivered today.
Also from terminal 3 you go to the center lug of the 9 pin tube socket. This is the ground route for the LEDs in the cathode circuits.
The power supply ground comes from those bottom headphone jack terminals to terminal 12. From there it jumpers to terminal 14 and ends at terminal 20.
The heater (AC) supply is a ground wire from transformer terminal 4 to terminal 22.
Ok, so all this means you should clip on to the chassis (which is screwed to terminal 3 the source of all the grounds). Tracing from the plate outward you should read zero to T3, Volume 2 left lugs, both RCA outer conductors, headphone jack bottom terminals, T12, T14, T20, center pin of the 9 pin socket, and to T22.
Other grounds that should be solid are pin 8 of the large tube, pin 4 and 5 of the small tube, T8, T11, T14, T16, T17, T20, T21 & T22.