Looks ok to me, as long as the box is that far above the rear tires the load is not too much. Think about it, when a truck is overloaded the front is way up in the air & the back end is way low.
only reall way to tell is to look at the front end up close from underneath- depending on the year it could be leaf springs up front or coils- leafs go flat or some times break one or more of the leaves, coils either break or punch through the tower.
That era of truck 2wd were low in the front, especially with a diesel. It has coil springs with "I" beams for suspension in the front. That truck will take the weight
Ummm most front ends are lower. And no they dont squat evenly under a load. The rear is higher when unloaded so that when a load is put on it it tgen more closely matches the front.
My 3500 dodge sat 5" taller in the rear. I put a 2" lift on front to get rid of the raked look but still have a few inches to squat to level. I also did it to clear 35" tireswelder is 1500lbs and puts my pickup about perfectly leve. Most trailers i pull also level it depending on the load on trailer.