If you can find a complete 20ez, and they do come up fairly often on KLOV, that's going to be a much easier repair. You've already done the hardest part of a 1-for-1 sayno 20ez swap - removing it from the cab.
Going to LCD, aside from the taboo of it and of course input delay and overall playing experience downgrade, which should be enough to not want to do it
, you will need to:
1) Get a NIN2JAMMA and something like a GBS-8200.
2) Connect NIN2JAMMA to unused edge connector on DK PCB.
3) Wire RGBS and power from NIN2JAMMA to GBS-8200.
4) Figure out how to mount the LCD in the cab.
5) Run VGA output from GBS-8200 to LCD.
6) You will also need to power the LCD somehow, probably just running a power cord out of the back of the cabinet (the outlet at the bottom of the cabinet is 100V, may or may not work to power an LCD, not recommended).
:edit: not sure how and LCD converted but otherwise original cab score would be received. Will leave that call up to the almighty jry.