I'll post some results asap. There's full coverage for 9x12 negatives, I'll wait and see about the 4x5 format.
As to why I didn't choose a nicer model, it's because these cameras are quite scarce in Denmark. And shipping + customs charges from other countries add to the price. So I just bought the first one that showed up.
I don't know how I'll adjust the rangefinder, but I'll figure something out. If nothing else, I suppose a few distance marks on the upper strut could do the trick.
The system with the aluminum rails works fine: no light leaks at all.
Keytar: Good luck with your project.
The Ektar lens is heavy, so the camera turned out a bit heavier than I hoped, but at least the shutter was very easy to service.