depends how much effort you are putting into it, but even the basic casting resin should do the trick fine. but if you are making a upc rubber mold which is the more professional might be worth looking for a urethane type casting material, there are so many that could do the job. just don't buy one that recommended heat or vacuum chambers to set, most of these new products dont now.  again if you look at those vids on that link above, it does talk about various casting resins and mold techniques, there will be allot of satisfaction having reproduction inserts in your playfield you made your self, that would be awesome.