The variable PARA_ARCH only changes the output of sysname. If you just set it and don't use sysname afterwards, nothing will happen.
It can be seen as a two-step strategy to tell the OS, where to find scripts or binaries.
First, set export PARA_ARCH=SMP and then export PATH="${TURBODIR}/bin/`sysname`:${PATH}".
With this, the path is set to the SMP version.
Cheers,
Arnim