As the chemistry is fairly expensive (far more so than the cheap RA4) it might make sense to use new paper and new chemicals. At least your results would be repeatable doing that. There is/were a couple (maybe only one, but I can't remember the name) of labs in Oz still producing Ilfochrome - maybe you could approach someone there to make a few prints for you ?

A couple of decades ago I used to work in a lab including producing internegs for positive-to-RA4, projection printing with 5x4 darkslides to hold the interneg C41 film. We never did any Cibachrome/Ilfochrome so that was our route to prints from transparencies. I doubt the copy-film is still made these days

If you go with C41 film after all, then have a look at Ektar.