Both players have signed on one-month loan deals, and manager John Ward is delighted to have strengthened his squad with the two acquisitions.
The former Carlisle United boss told the club's official website: "Will's an American boy, who is very highly thought of Birmingham. So much so, that they don't want to get him cup-tied.
"Alex is a Swindon boy, so he knows this part of the world. He's a young winger looking for an opportunity to get going.
"There's not huge experience behind the boys, but they compliment the group and want to enhance their own careers."
Packwood and Henshall are expected to feature in the squad to face Wycombe Wanderers on Saturday.