That modification on Eric Klein's machine is interesting because it is the first (and only?) modification known on a Kenbak-1. Common sense suggests that this should be an input or output, the only thing that a Kenbak-1 lacks to do "real work." We've probably all wondered how to make an input or output (of course, Grant's investigations show the light lines can be used, maybe with a low-pass filter.)
I seem to recall that Herbert Eisengruber (Nova Scotia) had some type of machine interfaced up to a Kenbak-1, but maybe I just dreamed this up. At one VCF meeting, in the pictures, I thought he had some later hardware that was hooked up to a kenbak-1, but now I can't find a source, and the pictures don't make that clear.
Look at this picture....
http://home.comcast.net/~msmith6020/P7160223a_copy.jpg
towards the bottom right of the picture is a photo showing a kenbak-1 with a later box on top of it. Was this a input/output interface? If anyone knows Herbert, maybe they could ask him. Herbert's machines came right out of a technical school, so I wouldn't expect them to have the modifications such as a privately owned machine could have attained.
In any case, maybe we'll never know details of why Erik's machine was modified, as a whole-big circuit board with lots of logic could have been interfaced into those few signals, and all that is long lost.
Oh, and Grant: I didn't get to the bank before they closed, so no money order. I'll definitely get it mailed by Saturday, priority mail. Don't give my kit away to anyone else!!!