you will get the best job if the whole thing is taken down to clean bare metal, and a bodyman can minimize filler with good metal bumping when it's clean and bare
I've had parts redi-stripped - doesn't 'ruin' the metal, it cleans it 100% ... it can however leave residues in hidden joints like the pinch welds, so it has to be rinsed properly, and phosphating afterwards is advised .... I'd use chem stripping on some things, sandblasting on others, complete cabs is where the biggest problems can occur
OTOH, sandblasting leaves sand in those same hidden places, and some folks have had to deal with it vibrating out of joints for years, need to be careful about sandblasting inside cabs
Bill