Finished off the diff cooler and re-installed the fuel tank. Everything clears, nothing interferes, yay!
Tomorrow I fill er up and prime the diff cooling system for the first time. Check for leaks, etc.
Also cleaned the fuel filler neck of 20 years of road grime. Took a pneumatic wire wheel to it, slathered it in acetone, then painted it a couple coats in the sunlight. Gave it a new body gasket because the original was worn to hell. And found during the course of all this that Ford's self-tapping sheet metal bolts holding the gasket to the body had worn out the sheet metal so bad that they no longer threaded.
Drilled the 4 holes out bigger and welded some flange nuts to the top side, inside the trunk. This was of course with the fuel tank moved into another room and the roll up door completely open (fumes). Had some real nice stainless metric bolts lying around and so put them to good use on this body gasket. She's good as new.