A) This is the Rosetta++ board (Rosetta 2.x), you probably meant to post this on the Rosetta 3.x board.
You should try asking around on scons sites as well – this is really a scons question not a rosetta question.
C) I would try naming (or symlinking) YOUR gcc’s something else, like my_gcc, then editing scons to use my_gcc instead of gcc. It will never find the default gcc’s, since the name is now changed, so it’s forced to go look for yours.
D) You may want to examine the cxx flags. I know you use cxx=icc on the compile command line to get intel compilers; I’ve also used cxx = gcc### (where ### is a version number) to get rosetta to use a particular installed version of gcc when there was more than one available.