[taildragger]

I don't mean to be a logistics wonk but...

Why not retrofit the C-5 with the F117 engine (P & W 2040) that the C-17 uses to reduce your spare parts inventory?

Granted a little less thrust, perhaps an upgrade/push would benefit both airframes.

Now if it was a hybrid pylon down upgrade and used the C-17's Nacelles and reverser's that may be sweet.

[Paleo Conservative]

Why not retrofit the C-5 with the F117 engine (P & W 2040) that the C-17 uses to reduce your spare parts inventory?

Probably because the TF-39 used on the C-5 was the ancestor of the CF6-80C2. The engines are similar enough to not require major redesigns of other subsystems on the C-5. They are also similar to the engines used on Airforce One and the E-4B's.