The Ten Pace Boots are invisible for me (when worn). So far I've got Morrowind Patch Project 1.6.4 installed (which lists this issue as being fixed), and I've tried manually replacing the file /Meshes/A/a_tenpaceboot.nif with the one included in the MPP zip file, but it's still invisible. (Sorry if this is the wrong place to ask about this.)

Have you tried a clean save, with no other ESMs/ESPs enabled, and adding the boots via the console?

I've tried starting a new game with only the expansions + MPP 1.6.4. enabled and then adding boots via console and they're still invisible. Same thing happens without MPP 1.6.4.