4L60E's weight comparison
 

For what it is worth... i had the original lt1 4L60e until the torque converter weight came off and split my bellhouse so i switched to the ls1 split bellhouse 4L60E for a while but i didn't like the way it fit and looked under there... i also thought it felt heavier so i decided to go back to the lt1 4L60E...

In doing so i decided to way both transmissions without the torque converter and found out that the ls1 4L60E weights 148.5 lbs and the lt1 weights 128.0 lbs... 20 lbs less...
It seems that where they saved weight with the aluminum block they then added weight with the transmission...
Just some food for thought...