An update. I updated the settings on my HxC from "Auto" to "Generic Shugart". I'm now able to boot the CP/M Plus image from the archive.

Formatting a floppy in TRSDOS 2.0b still doesn't work (during format it counts up the sectors for track 0 and then from track 1 and up the sector stays stuck at 26). Formatting in P&T CP/M formats up to track 77 now but fails when verifying at track 44 saying the sector isn't found.

Speaking of CP/M Plus, the image in the archive is the Unbanked version. Does anyone have the Banked version?

It looks almost exactly like the Model 4 version. It doesn't seem as slow, though, so that's an improvement.