I don't know if this is what you are looking for or not, but why not ortho lith film? enlarge and develop it as you would normally with a slightly diluted developer - my experimentations took quite some time to get the right tone and contrast out of the developer, but in the end, it can result in quite a decent positive image on film able to be mounted then to a choice of backgrounds. for my purposes, i have mounted 40 x 60 inch panels onto a gold leaf backed glass for my "fauxrotones" of the los angeles river.
if your intending to put them in a light-box, i'm not sure the lith film would be dense enough without getting way to contrasty to yield good dark blacks. (again, a project i am working on involves light boxes and i'm getting interesting results with some different papers).
just some thoughts - if you need some info on the lith film, look into freestyle or pm me.
matthew