In today's mail I received a Zenith 163-73. It has yellow Alps and dye-sub PBT caps. It is XT/AT-selectable via a DIP switch on the back of the keyboard. I am typing on it now in AT mode. The yellow switches are quite smooth and reported as slightly heavier than green Alps, but I have not yet tried them side by side.
The board is very clean with no corrosion on the plate. It also feels very solid. Unfortunately, there is one key that responds only intermittently -- the Backspace/Pipe key to the right of the shortened Right Shift. This is particularly unwanted, because I plan to use this key as Fn. I am hoping that the key will become fully functional after cleaning -- including using a contact cleaner.
I am also considering a click/tactile mod, but I first I want to test out the board thoroughly with unmodified switches.
Suggestions welcome for a possible click/tactile mod. I am not sure which components (slider, top housing, spring, tactile/click leaf) would be compatible with the bottom housing and switchplate in yellow Alps.
Some potential donor Alps or Alps-clone switches that I have available include black, blue, damped cream, undamped cream, white, damped white, Matias Click, and Matias Quiet.
I did have quite a few brown Alps in IBM 5140 boards, but I've been selling these, and the last one is currently collecting bids (I found brown Alps a bit too stiff for prolonged typing).