GM 'o7classic LBZ dsl 6 spd to '21 L5P dsl 10 spd report

4 1/2" sounds close, its not an issue in a dip it is in an hilltop. What we in pipelining called an overbend, vs sag.
The tailgate to overhead of the 5er contact with a 8' bed would mean a 20% overbend hill top I agree, not ideal , unlikely. avoidable. Raising the 5er is an option, that adds even more complications.