Found it! The e-mail address of the seller was joe@signedautographs.com but I do not know his eBay ID. I sent him an e-mail asking how he knew the base was the actual one during that inning when A-Rod made the slap (since they use more than 1 base) and he replied saying:
"
There were only two sets used for that game, switching in the 5th inning
Arroyo happened in the 8th inning...AND the MLB authentication says SET 2.

Thank you,
Joe"

He sent me the e-mail on November 3,2006. eBay item number 320044767517