it depends on what kind of engine you have. I can't remember the term- impact and non-impact, something like that.

anyway, the LS engine you have I believe, is a non-impact engine, meaning the valves should not have hit the pistons.

I had a thread about something like this a while back, but I can't find it. Its when I snapped my timing belt on my LS. If you have somebody with patron priviledges, go back in the tech talk area around 2005 or so and do a search for my thread. it was very interesting and it might help.