Very good question, I wish I could answer it for you,
Last month I had the opportunity to tour the St. Catherines engine plant in Canada (they build our LS1 & LS6 there). That would have been an excellent time to get your question answered.......maybe some one else knows.
JT, in August during the engine plant tour, I did an interview with quite a few of the plant workers. The weight of the block did come up at one of the first stations. We were told 110 lbs for the block. My guess for the total weight would be around 300 lbs, but I did not ask for a specific finished number. Next time I will. How important is this to you? I could get the answer faster for you if necessary.