Where's the thermocouple going to be mounted?
Right under the inlet bearing, of course.
Py,
Do you know why the new screws won't fit? If it's only a matter of length, then I would try to take the old ones to a good hardware store, have them match the thread and go longer.
I'm not familiar enough w/ metric to know if they actually have a fine pitch thread. SAE threads have normal and fine, but I've never heard of anyone referring to metrics like that. I'd suggest calling a couple of those websites you listed and picking their brain. The screws listed are all cheap enough that you could buy a few different sizes. I'd also suggest the socket head screws instead of the hex head.
The last thought would be to simply leave the grinder as it is. Not to start a war, but stepless is overrated.