Yeah, if he really put 9 qts in the crankcase, your engine will be toast in no time. With that much oil, the crank will almost certainly whip it to a lovely froth, which means the oil pump will start sucking air, and your engine will die of oil starvation.
The 2nd Gen LSes, with the oil coolers and VVT, take ~6.5 qts, but the 1st gens only take ~6 qts. Either way, 9 qts is way too much.
Beamer's right drain it and refill it yourself.
One thing that occurs to me, though no respectable mechanic would do it, is that he might have filled it with the engine running. In that case, he could have put 9qts in the engine, as a goodly portion of it would be up in the valvetrain...