I posted this on the chevy chapter already, but maybe someone will see it here as well. I have a 6" BDS lift on my 99 Silverado, I saw a similar set up with a 2" torsion key lift added to it and wondered if that would work? Like what are the cons of it? Also, I have the replacement springs for the rear, can I use an add-a-leaf or blocks with it to raise the rear as well??  

These keys have been covered a lot and should be avoided. All is not as it seems. They place suspension at or very near top of expansion travel or front wheels which can result in a pitchy ride and it throws suspension geometry out of whack too.