Get the gcc48 compiler:
pacman -allow trust-all-caches -get http://atlas-computing.web.cern.ch/atlas-computing/links/monolith/whole/Generic:gcc481_slc6
Get SLC6/64b/gcc48/OPT kit:
pacman -allow any-platform trust-all-caches tar-overwrite -get http://atlas-computing.web.cern.ch/atlas-computing/links/kitsDirectory/projects/cache:AthSimulationBase_1_0_2_x86_64_slc6_gcc48_opt
Grid/CVMFS: distributed
Other comments: trying out a simulation-only release on the grid.