Leveling coil spring spacers for 2WD trucks

I'd like to raise the height of my C2500 (not a 4x4) by a couple of inches to level out the ride height. I've seen these 1.5" polyurethane spacers that fit over the top of the coil springs. Is there a downside to these? Do they put the torsion bar under greater stress, or stress other parts of the front suspension?