I never read manuals, I just ask on forums...
But it did occur to me to call CPS, and it turns out, focusing screens are a thing of the past, sure enough.
That's curious, but interesting.
But there *is* an electronic version of it, that you can turn on in the menus. Works good, I'm all happy again.
For my edification, what does it offer? I use a different focusing screen in my 1Ds3, because the physical characteristics of a different diffusion (better DOF estimation and manual focus accuracy with f/2.8 or wider optics) cannot really be compensated in software (as long as the viewfinder is all optical).