magnum factory exhaust sizes question

The magnum engine was never released in Australia. Only the LA engines were.
So i cant buy magnum stuff here and if i ship second hand parts or parts from junk jards it can be difficult to get clearance.
Just trying to find the best flowing exhaust. I could buy block huggers if they flow as good. If i could find new ones they would be fine to ship. If i cant find new ones i may just have to take a chance.