Martin -
I think an old thread had weights of the SVO and DART (No Man O' War at the time) in iron and aluminum.
Take a look at
Home of GTSparkPlugs.com Go to the cars button and look at the Tiger pages I think you can see the side of the Dart block on the engine stand. Also they are easy to spot vs. the Iron versions of stock 302's. Freeze plugs, different Oil sender area, and the shiny color give it away. If you are trying to squeeze it by a tech as original likely will not happen. The SVO aluminum blocks also have a nice Tattoo on the front of the block.
Sandy