Cant be 600#. M113 = 413 fully dresses, M120 = 654 fully dressed. There is a reason the 0-60 times of the R129 SL600 and SL500 are about the same. M117 ~ 500#
I would like to get a good number for the M104 to add to this thread.
http://www.peachparts.com/shopforum/performance-paddock/174184-motor-weights-2.html