I took the info that I could find on the forums via "search" and added my own successful alterations to the process of replacing the clock's clear plastic face,...
This pic is pretty self-explanatory:

Transparent tape over the bezel to prevent scratches. I used my needle-nose to hold the shaft securely, while pulling off the knob. The shaft has splines,...
I have some flat needle files that have smooth edges, so I used them to file down the crimped edge of the aluminum bezel (rather than bend it out, or cut it off, as I had read about before). It worked quite nicely, leaving a smooth edge on the side of the bezel.
Once the bezel could be worked loose from the plastic housing, I replaced the clear face and bezel. I then painted the outer edge of the clock housing with black paint (~ where the crimp used to be) - enough to disguise my bezel alteration,...
I used a tiny bit of E6000 adhesive (remains flexible) in a couple of spots on the rear of the bezel to secure it to the clock housing (although it fit pretty tightly). I re-installed the adjustment knob the way I removed it - securing the shaft with the needle-nose. Then I pushed the knob back on with my thumb.
Results: 1979 factory dash:

BTW,...did you know that these speedometers had physical stops at about 4mph? The speedo does NOT go to zero,...! Odd.
I sure hope this helps some folks!
Todd.