Revised 3/28/14, 4/19/16, 9/13/16
Documentation and code at
http://docmesure.free.fr/manuels/Tektronix/Serie%207000/0scillos%207000/7854/7854/roms/

Remove U100 and U200.
Program 27128 adapter for U200 from 7854MSB.PAT and (use U200 location for clearance).

Remove U110 and U210.
Program 27128 adapter for U210 from 7854LSB.PAT and (use U210 location for clearance).

Wire A13.
Connect from both 27128 pin 26 to U425 pin 1.

Wire new CS.  Note: you have to disconnect the old CS from U200 and U210 pin 20 (note CS is the nomeclature for the ROM).  I did this by not connecting pin 22 in the EPROM adapter (which is connected to pin 20 on the PCB) and then running the following wire directly to pin 22 of the EPROM on the adapter.

  Option 1:  Add an unused gate.
  Connect from both 27128 U200 and U210 pin 22 to U225 pin 11.
  Connect U320 pin 13 to U225 pins 12 and 13.

  Option 2: (note I did not do this one so consider it unverified)
  Cut and lift U420 pins 9 and 13.  They will float high or you can connect these pins to +5V

Remove FPLA U120.  The information is embedded in the .PAT ROM files.

You must have the patch ROMs that match the main ROMs.
Reprogram 2716 patch EPROM for U400 from 7854PAT.MSB.
Reprogram 2716 patch EPROM for U410 from 7854PAT.LSB.