To re-stir the pot, I have a 90 f6.8 Rodenstock on a Shen-Hao. It is a fantastic combo (I also happen to have a Keith Canham gg w/ fresnel in place of the factory gg). I found mine on Ebay like new with original box for $450 +/- . I would prefer the 6.8 to the f8 for the brightness but more importantly the additional coverage. With the exception of the Nikon 90 f8, all the f8 90mm lenses currently out there have significantly smaller image circles than the 6.8s and 5.6's/4.5's. If you're going to be hiking with the lens, and carrying more than one or two other lenses with you, I'd suggest the 6.8 or the f8 Nikon as best bets.
If you go with the Fuji 4.5, I don't know if the 80mm rear element on that fuji will fit through the front standard or not - would be a bit of a tight squeeze. You might have to remove the rear element, mount the lensboard, then re-attach the element from inside the bellows. As to filters, you can always get a Lee gelatin filter holder which will accomodate up to 87mm diameter lenses I believe. Maybe even 92mm. The Lee gelatin filters are excellent, and inexpensive. They make one filter holder which goes on using a big rubber band, and costs about $20.