I was able to successfully get the two-step upgrade.
I ended up with two serial numbers. One for Pro and one for Ultra.
I had to manually replace the Pro Serial Number (in the secret text file) with the Ultra Serial # in order to populate the download Manager in BIAB Utilities with the 120gb of content.
After three days of 24/7 downloading I have three files to go, so I beat the arrival of the physical drive.
This thread was lots of fun. You guys are the best.