keyway torsion bar lift

i have a 1995 gmc sierra 4x4 with a 3 in. body lift and 33 in. tires. i want to fit some 35's on it and saw the keyway lift for 59 bucks online. im thinking about putting it on with a 2 inch block in the back to make room for 35's. just wondering if this is smart idea and if u guys kno anyway who has done it.thanks