You need to get papers verifying where that wood came from. A dated letter from your friend's uncle stating who he was, what he did at the ranch, where and how he got the wood and its connection to Sea Biscuit should do it. It would tremendously increase the value of the call. If it was notarized or witnessed, it would be even better. I know you may not plan on selling it now, but it would hold a lot more value that way if you grandkids or somebody inherited it and decided to sell it someday.
Whoda thunk I'd learn something from those pawn shop dudes on the History Channel?
BTW, that's a VERY cool call!