I have tried reversal processing RA-4 paper, using a FD mix it yourself ( and in this case let stand for a few days too) recipe Ron Mowery gave me.
Then after the FD, rinse, optically fog, and feed into my rollewr processor like an ordinary print.
The process works, but getting the colours and contrast right has not beemn good enough to call this process viable.
I have a few hunderd feet of Fuji IT-N, and a an illumitran duper for copying 35mm slides.
For 120, and 4x5 transparencies I flip a spare Omega 4x5 dichroic head under an old Polariod copy camera and reduce the slide to a 35mm interneg by long exposures of balanced light while the room is otherwise blacked out.
It has to be an image I really want to see. The process is a hassle.