JBaird,
My measured figures, with flywheel and carb (+/- 10 lbs) are:
All iron FE - 610 lbs
Iron block, aluminum heads, water pump and intake - 520 lbs
All-aluminum Shelby - 460 lbs
Which would indicate only a 60 lbs difference between the iron and aluminum blocks... Things are not adding up.
My guess is that the Shelby figure doesn't include the sleeves and bearing caps.