Experimental Me! I obtained today, and am using right now, an IBM Terminal board 1392595 with a 1993 1391401 controller on it. Every key works, including the "RESERVED" key below the + on the numeric keypad. It's in remarkably good shape, but the keys do need to be cleaned. The pictures will show that. No worries I will clean it up.
This is only the beginning. I did get an APL set from Unicomp too. I'm expecting that later, so I may just put those key caps on this board. It will look clean!
I might do the LED thing. I may just leave it alone.