Further investigation leads me to think that the righthand spacebar linkage (attached to the underside of the spacebar itself) is binding on the slot where it passes through the sheet metal cover and into the machine's interior. I've tried to form the linkage enough to clear the binding, but without success thus far.

I think I need to get under the sheet metal to get a better purchase on the linkage to form it. Doing so looks to be complicated by the fact that the front of the machine (under the keys) is a series of stair steps, which adds to its distinctive look. Each "step" if you will is held down by a screw at each end, but because each step is slightly overlapped by the one above it (i.e. moving toward the top of the keyboard), I may have to remove or at least loosen each set of screws to be able to get underneath the bottom step where the spacebar linkage enters the innards.