The B-52 was a test bed in the 70s for 747 and C-5 engines
https://aviation.stackexchange.com/questions/74192/what-is-this-large-engine-doing-on-a-b52

Not to hijack, but I was kinda saddened when I learned the C-5's don't have the TF-39s anymore.

B-521.PNGb-522.PNG