My first (so far) LED backlit Model M.
http://www.ebay.com/itm/331398234297The LEDs are controlled with the Scroll-Lock key, I wired the LEDs into the trigger circuit for scroll lock so you can toggle it on or off.
I am pretty happy with it, and there were no permanent modifications to the chimney plate, you can take the LEDs out if you wanted, and the plate would be unharmed.
I think next time I won't use one with a black chimney=plate, and I will also not use one of the newer Lexmark ones, since they have little raised ribs that interfere with an even coverage of light. I will probably make the next one with green LED backlighting. We shall see...
Blue LED glow:
Looking great even when the lights are on.