I did sim training on the Classic 747 at NATCO in 2004 - I had HC, a retired NWA Captain as the contract instructor (great guy) - he mentioned at some point that the company he owned which did industrial testing for companies tested the 747 scavenge pump after the accident. They tried every which way to get that pump to ignite vapors in a test cell - never could.

The classic whale had an AD that came after the accident to use the center tank fuel in various ways to avoid creating what the FAA thought was an explosive mixture. Once you reached 1000 pounds in the center, you used the scavenge pump to pump it to one of the main tanks.