Shoes supporting heel-mounted cleats
With the help of a bike fitter and mechanic, we found a very good solution that has served me well. I've put in about 2000 km this year and am heading to my first imperial century tomorrow.

Mechanically, the solution involved:


Custom mounting SPD cleats quite far back on the soles. I'll add a picture later, but I'd say they're 3/4 of the way to the heel. For my torsioned leg, the cleat is mounted rotated by 35 degrees.
Carbon-soled road shoes with a flat surface to the back. We went with Bontrager Velocis. First attempt was with non-carbon soles, but the sole ended up tearing under pressure after a while. I've found the pressures do loosen up the cleats so I've had to have the mechanic tighten and glue them twice over the season.
Kneesavers pedal extenders - To avoid hitting my heel on the crank arm, we put in the longest pedal extender for my torsioned leg, and a shorter one on the other side for balance (to avoid feeling off centre on the seat).


From there, bike fitting was key. Everything is configured so knees, hips, etc. follow the usual parameters as much as possible.

So far, I'm feeling great, and don't really notice the loss of calf muscles in the pedal stroke. Some occasional knee soreness, but nothing beyond what I think most 40-year-old cyclists experience.

Very grateful to my local bike shop for taking lots of time to come up with this custom solution!