I don't know his sig enough to give a confident yes or no; but that database did make my concerns (the strange S, the narrow loop at the end of the first name, the g) go away.
Thanks, JXE. There are a number of similar characteristics so I can see why this might be a difficult call for PSA. The leftward looping "w", the occasional "stretch" between the "wi" in "wishes" are consistent with King. Not sure about the "8s", there's an almost intentional pause on both. Also, the handwriting doesn't slant near as much as other later examples I've seen. Thanks for weighing in!
Two additional sources, including Rocky Wood, widely regarded as the leading expert on King's work, and a King book collectors group have both said they'd avoid it as well, unfortunately.