Summary:

This article shows a comparison done between the MAC, JBA, and stock headers your Mustang.

Details:

Both test were run on a STOCK 5.0 engine.
All the headers tested are SHORTIES.
The chart shows that the MAC Equal Length shorties of 1.5" and 1 5/8" deliver the most torque and HP.
On a NON Stock motor the 1/2" headers might be too restrictive.

The JBA headers (most expensive of all) are the bottom performers on both charts.