Hello Ross,
You can create MPC5676R project in the Project Wizard and remove/delete all source files.
Then you can e.g create and add to project:
__startup.s file which includes __start routine ...this is where you can add your startup asm code. It jumps to main_asm() at the end.
And main_asm.s this is where you place your main code.
You can create your own project structure - this is just an example (see attached project).
Hope it helps.
Stan