Very interesting. I'd love to see the card in person. The stamp looks good to me. The cracking on the paper is very suspicious. I'd be interested in Rhett's opinion.
If it's real, it's a tough card, only a handful known, probably the second-most important card in the set next to Ruth.
Edited to add: the known fakes are DEFINITELY discernible from the stamp. The ink color is the same, but the typefaces are entirely different. Picture below.
-Al