This mod turns a helpless 12h analog clock into a dashing 12-at-the-top 24h analog clock.
Total cost: ~$33.75
For the wall clock, I picked up one that matched our kitchen's decor. This is a white, generic 12" clock from Target, (SKU 490651513545). This particular clock's face diameter is 28.3cm, so I adjusted the clock face printout for it.
The removed 12h clock movement. It turns out that these quartz movements are remarkably standardized in their dimensions. The 24h movement I got is not very different in size from this one.
A white paper mask cut to cover up the old 12h numbers. This will prevent them from showing through, even if the new face is printed on thin paper.
I had the face printed at Kinkos on their oversized printer, as it was just a bit larger than 11x17" with the dotted line around it. It wasn't the best print job and the paper was thinner than I wanted, but it seems to get the job done. Next time: design it so it will definitely fit on 11x17", as everyone can print onto that size.
Both hands and face installed.
I decided to use spraymount (a type of weak glue that comes in a spray can, usually used for movable fixtures) to join the the clock face printout to the white mask. This reinforced the face so it was rigid, while masking out the old numbers. Due to this rigidity, I didn't need to affix it to the clock body permanently. As is, the screw that holds in the movement also holds on the face.
The hand installation was straightforward. I had to use two of the rubber gaskets that sit between the clock movement and the clock body, as the 24h movement's post was longer than the original movement's post (it was touching the glass).