I found one of the culprits that bloated my boot drive following installation of SP3. It is a Windows folder called ServicePackFiles. It is around 480 MB. From what I was able to find out, it should not be removed.

I think I am looking for the SP3 uninstall files. I can't locate them. Since the ServicePackFiles folder contains all the old files replaced by SP3 maybe they are the SP3 uninstall files. Maybe there is nothing to remove to restore the drive to pre-SP3 size.

It did not take three boots for my system to be fine. It was fine after the first reboot. What I was trying to say that after three reboots I had no problems.

I do not need backup files. I have pre and post boot drive images on another HD that I can restore if necessary.