Just completed task on my Tartan 33. I agree that you should visit your local sign person. The "raw" material is basically the same no matter where you go but I opted to have them install it! It was well worth the few bucks extra. I too have a slight arc/curve to the upper transom and it was very tricky to position. Local sign shops also have greater variety in typeface designs.
Just a couple of notes: a shadow effect might cost you extra, also takes up a bit more horizontal space; avoid script if you have a documented boat (IMHO); boat name for a transom your size could be about 6-6.5" with hailing port 4"; polish surface before application but wax "after"; while typeface designs are a preference call, the basic sans serifs look pretty plain, on the other hand extreme serif fonts can look too cluttered. You should get out of the deal, with their application for under $200.