I know I said a few other things in your other thread
but
besides the fact that not many people will sell them...
I was working on my XC bike today, it runs Manitou forks and a 7" XT disc. Now, having a close look at the spacing, if post mounts have the same dimensions accross all forks, you're going to have a very hard time trying to get the rotor to clear the actual posts. I have only a few mm between my rotor, and the post, measured vertically. So unless the manitou forks in question are designed for 8" rotors, you'll have an impossible task fitting one on.
By the way, this is just a one-off example, forks may differ, I haven't had much experience in this situation, I'm just pointing out what I've found with my forks.