All those things don't necesarily add up to a previously wrecked truck imo.....lamps always sprout a leak here and there, no matter wrecked or not. The leakage could have changed the colors alil bit too. Could be as simple as an accidental bicycle handle bar hitting the corner lamp, causing a crack/break, and aftermarket replacement installed. Same could go for the taillamps.
The engine deal....well.....heavy oil into an engine that takes thin oil....causes bad things to happen...so new engine is a new engine....new truck pretty much!
That driver rear sag.....how's the alignment of the bed and cab? is it square to the cab? looking from the back, is the bed aligned with the back window? Could be as simple as being a bad spring or bad bushings.
'01 XLT disguised as a '03 Fx4 Level II
Big. Loud. Slow. Bright.