OK, finally got things straightened out.
After downloading and unzipping, rename "sam-1.6.4.tar" folder to "sam"
and save it at
C:\Program Files (x86)\arduino-1.6.5-r5\hardware\arduino
After downloading and unzipping, move
"arm_none_eabi_gcc" and "bossac"
to
C:\Program Files (x86)\arduino-1.6.5-r5\hardware\arduino\sam
open the "platform.txt" file in C:\Program Files (x86)\arduino-1.6.5-r5\hardware\arduino\sam
and make the following edits:
compiler.path={runtime.ide.path}/hardware/tools/arm-none-eabi-gcc/bin/
#compiler.path={runtime.tools.arm-none-eabi-gcc.path}/bin/
tools.bossac.path={runtime.ide.path}/hardware/arduino/sam/
runtime.tools.bossac.path=tools.bossac.path
#tools.bossac.path={runtime.tools.bossac.path}
Open the Arduino application.,I can't recall whether I re-ran the Boards Manager (under tools)
or if the Due appeared in the list of boards.
Good luck!