Nah. Sounds fishy to me. Two problems I see. Neither cyanotypes nor blue toned prints are archival. RA-4 prints would look like, well, RA-4 prints even if you can get close to a color match. I think the best thing is to make the prints of low contrast on a good fiber based paper. Tone them with selenium or sepia toner if you want a warm or aged look. You don't want that high contrast, edgy look that's so easy to get with modern materials. In the end you'll have a collection of prints that will look good and complement the already existing archive of prints. Properly processed, they will last a long time and provide a record for the future.