Short Version:

For me, an 8 GB USB 2.0 Lexar Flash drive worked after a Sync "master reset." The successful run took about 20 mins. The version update was from 1.0 to 2.2.
-The flash drive was quick-formatted to EXFAT (32-bit)
-I had opened the Sync upgrade zip file on my desktop computer, then transferred the contents (two files and one folder) as-is to the flash drive.

Long Version:

I first tried this with a 32GB Lexar Flash drive. The first time I let it go for 30 mins before pulling the plug. The second time I let it go for 45 mins before pulling the plug.

For the third attempt, I decided to do a 'Master Reset' first, based on a post that I read here. I also decided to try my 8GB drive for absolutely no good reason (both the 8GB and 32GB drives are USB 2.0, formatted to EXFAT as per Ford's instructions).

At the 15 minute mark I was preparing to give up, but decided to give it five more minutes, as the majority of posts that I had seen here reported it taking 15-20 mins. Pretty much right at 20 mins, the screen changed to the "Complete" message. I removed the USB stick, shut the truck off, left it to sit for 10 mins, started it back up, and Android Auto was there.

Thanks to everyone who posted what worked (and didn't work).