I ran across this comparison of engine weights - complete engines less bellhousing, flywheel, and clutch. Think DZ vs L78 vs L89 vs ZL1. This is comparison of nominal weights - a L78 vs a LS6 vs a L88 are going to have some minimal weight differences.
All variances (in parentheses) are from the iron small block.
Small block, cast iron - 520 pounds
Small block, iron w al head - 480 (-40)
Small block, al head & block - 389 (-131)
Big block, cast iron - 754 (+234)
Big block, iron w al head - 660 (+140)
Big block, al head & block - 501 (-19)