I weighed both my SBF 331, which used a 1973 production block, and my Dart blocked 347, and the 347 was 35 pounds heavier. Be aware, that these were complete carb to pan engines, and in addition to the differences between the 2 blocks, there were some other pieces that were different between the 2 engines. The 331 had a cast crank, stock timing cover and water pump (aluminum 5.0 Mustang pump), Victor Jr. intake and Comp steel roller rockers, where the 347 has a steel crank, a Jesel timing belt drive and Meziere electric water pump, and a Parker Funnel Web intake and Crower aluminum shaft rockers. Not sure how much lighter the production 5.0 hyd roller blocks were than the early 70s 302 blocks, after the roller block broke, I went with a 73 block, I never compared the weights of the roller block to the 73 block.