Hi robbiedoo,
Sorry I missed this earlier. I believe that my plate came with an adhesive backing, so I just pulled off the paper and stuck it on. After filling the playfield with wood filler, and a bit of soft sanding. When I got my plate a couple of years ago, my distributor was able to order it directly from Stern. They may still have some, the service bulletin references each of those parts individually, so there is a specific # for that plate.
Good luck with X-files and feel free to let me know if I can be of any other help with it. I love mine!