I got the same thing, twice (I sent one to GB Enterprises, one to the Masters Locker Room), and they both look legit compared to the Leaf Metal Auto I pulled last year.
On a side note, I got another return from Arnold Palmer, also c/o the Masters Locker Room that looks far more legit than the usual autopens. I don't have anything real to compare it to at home, but the beginning of the A in Arnold doesn't have the same thickness the whole way through the curve that it seems to have for the autopens. Dan, your photo of the Jack/AP dual reminded me of that. I'll post some scans some time over the weekend.
tl;dr, I'm almost certain the Jack is legit, and that AP from the Masters Mens Locker Room could be as well.
Always looking for low # Eric Young Jr and Andrew Cashner cards!