I am restoring an Underwood number 6 and am using waterslide decals from "the virtual typewriter museum / typewriter decal shop" after working with him since two of the decals had to be custom made. He is based in the netherlands and the product is outstanding. the only problem that I have had with them is that I put the clear coat on too heavy and didnt give the decal enough time to set. The only drawbacks I can find about them is that the decal sheets are not "pre-coated" meaning that you will need to "seal" the decals yourself before you use them (I used testors decal sealant and painted the parts with rustoleum and clear coated with rustoleum). If you go that route, give the sealand 48 hours to dry to be on the safest side, and IF you decide to clear coat over it, use very light mist coats untill its covered. But to cut this long winded response to a managable size, the service is great (any mistakes in the printing, I sent a pic of it to him and he had a replacement right on its way), the "gold leafing" was spot on and the typewriter postcard was just extra honey in the pot, so to speak along with a few test-pieces included. if I missed anything of your question, let me know or I can send pictures of a finished product to show the decals "in use".

What about applying a decal to a concave surface? The really bad one is on the front of the typebasket on my Royal 10 and I don't want to mess it up because it's probably the 2nd most visible one.