Generally speaking, if all three of them SS gurus above (Kelly, Darryl, and Suprin) said yes, you can't go wrong.
Like most people, I haven't seen this decal before, but I know still another reputable collector asserting its originality based on his own long-time experience. Yeah, I can safely ASSUME its originality, but since it is only a handful of people here (however knowledgeable they are)that are positive about it, it's only natural that the majority of people without experience with it should disagree. Scepticism is a sound mental attitude for a collector toward anything SS or rare. SS stuff are so heavily faked that people tend to accept only known textbook examples. So, a rare piece or a variant requires some extra efforts for convincing people. That would be a pain in the ass. I think that explains the reason for its relatively reasonable price at the dealer's site. However, I too believe the price will go higher if the new book comes out great like SS STEEL. Well, that is what we will see pretty soon. I heard the book will be coming out within this year, so let's see how it will turn out.
Shu