I neglected to mention that before I put those on I put two 3"x3"x3" blocks of assigned iron on. It was unchanged then and that led me to go a little over the top.
The weight is very close to what I expected. A 12in. cube of cast iron should weigh around 150lbs. The measure of that cube in PTC Creo 2.0 is a weight of 149lbs with the assigned material being fe40..