The problem with using the schnieder, I assume coming off a beaulieu, is that there is a rear lense element that projects slightly further than the rear thread, at least on the lovely 6-66. The end result of mounting this on the H8 would be that you would render some rather expensive damage to your reflex prism when you try to thread that lense. Not that I have tried mind you, but it looked a too close for comfort. I have seen the rear of few angenieux lenses and they seem to be more workable in this regards, as their rerar elements are flush with the threads.
The Bolex H8 mount furthermore is not a true c mount either, I would have to look up the exact figure but the back focus is slightly shallower than it would be on a true c mount. From what I understand and what I have discussed with a venerable Bolex technician is that any lense stopped down past say f4 should work perfectly. Here is an article which tell you more than you ever need to know about the reflex system:
http://www.city-net.com/~fodder/bolex/truth.html
The only way you could get a true c mount on these cameras is swapping out the faceplate for a H16 version, which has other advantages besides, but like everything else in this world that costs $$$.