Hi Larry,
I have tried your suggestion, and it looks VERY promising!

I have found a second hand bellows, added a 50 mm. nikon lens, a slide adapter and a flash working in TTL.
it is still a crude contraption, and there will be a lot of optimizing work; but right non i'm able to scan lots of negs very quickly, and the resolving power is such that i can see the grain perfectly!
thanks for the advice, and as soon as i'll be able to fix all the small problems i have now, i'll post some images to you.
My biggest problem is: how to move the negative roll exactly one frame, without having to open the negative holder all the times.
Using a flash for illumination is eliminating all the problems related to mirror vibrations, and i can keep the aperture at around F11; but i cannot see the frame when i move it, unless i open the holder...
thanks again
paolo