With it being 18 years old, and being a buffalo car, I would think it was only a coincidence you started running 100 octane when the lines rusted out.
I would think it could have happened just the same if you continued running 87 in the car.
IMO, a SS line would be great if you plan to drive the car in winter, or shortly after winter (exposure to salt).
If not, I don’t see why an OEM line would be a problem, providing it can handle the pressure of your new pump.