This SB is 450 lbs, but it has aluminum heads and intake. It also has lightweight internals. A stock SB with all cast iron parts is about 550 lbs. Just depends if you include exhaust manifolds, flywheel, etc.

But bottom line, it is easy to build a BB engine that weighs less than a stone stock SB. A stroker big-block should be lighter than a stock big-block due to the lighter rotating assembly.