The LS9 is a very specific, high-performance engine from the C6 Corvette ZR1. It's designed for that car's chassis and features. The 1996 Impala SS has a completely different engine bay, different mounting points, and different ancillary systems (like the cooling system and wiring harness). You'd be talking about a complete frame-off restoration-level project involving custom fabrication of mounts, wiring, plumbing, and potentially even chassis modifications to accommodate the larger engine. The cost and effort would far exceed the value of the resulting car.