I have never personally used a 1-piece AFO, but one was recently requested. As such, I have not as yet tested this design on myself. It should be fairly strong though. I just took FIDIM 3, stuck the top and bottom together and smoothed/thinned the hinge and bumper areas. I intentionally left the ankle area somewhat bulbous. Since I don't have castings of your legs, I can't be sure that it is sized appropriately. It is better to have some extra space in there than not enough, believe me. Your ankle bone suddenly ramming into hard plastic is…unpleasant. I know…

You may need to spread the upper apart to accommodate your calves. If so, you can either use the ‘grab’ and ‘elastic deform’ tools in Blender's (free) sculpting mode to adjust these, or get a heat gun from the hardware store. Wear leather gloves, heat them up with the heat gun, and spread them apart. The Wagner Furno 300 and the Harbor Freight Warrior are two cheaper heat guns. They look like hair dryers, but they will positively burn you in a hurry. Just be careful. Air cool before checking the fit. Do NOT use water yet. Nylon will soak up water, and heating it after that with the heat gun will make the water boil--causing the plastic to bubble. Before doing any modifications though, I recommend that you print a hollow version of a brace in cheap PLA just to see how it fits. That'll at least give you some idea what you're looking at before you start.

PRINTING:

I HIGHLY HIGHLY recommend some form of nylon for these. I used Overture ‘Easy Nylon’ because it prints well and is very strong. Extrusion temps as low as 250C seem to work fine, but I'm printing at 300C now that I have the capability. No ill effects from that, and layer adhesion at that temp is excellent. Overhangs will tend to curl up while printing, so some level of print cooling will likely be needed, despite many tutorials recommending against it for nylon. I use a raft to aid with bed adhesion and warping. It helps tremendously. Carbon fiber nylon's layer adhesion doesn't tend to be as good, so I do not believe it to be adviseable for these. The only brace I ever had break was made out of it. Layer split all the way across. Plus it's twice as expensive as standard nylon. Once your adjustments are finished, soak the finished braces overnight in water. Dry nylon can be brittle, but it becomes somewhat flexible once it soaks up some water. That flexibility is what gives it its strength. ie, It flexes instead of cracking.