273 Commando Exhaust Question

We've started working on restoring my brother's 1967 Barracuda notch. His car is a 273 2 barrel. He wants to upgrade to the Super Commando exhaust system. I was wondering if any of my FABO brothers could help us with pictures and measurements of the rectangular valence cut out for the exhaust tip. His car has a single exhaust 1/2 round cut out which will need to be modified.