With a woefully underestimated increase in the payload, I removed a bunch of wall mass from the ISI.  It unlocked pretty easily and then I commenced to removing more and yet more mass.  But I got there with the table locking/unlocking quite smoothly with well within spec shifts.  A 10Kg D0901075 even had to be removed from the table top.  In the end, the added payload & balance mass is lower by 52.45Kg.  I have red-lined D1001132-v3 with the changes and current mass distribution and added that to the DCC.

The ISI is unlocked with the C3 covers pulled away from the ISI.  HEPI remains locked.