I contacted Flowmaster about why they don't make a catback with the super 44s for the 99-04 stangs and got an interesting response.
"We use the super 40's in the system because we found that those mufflers preform the best and sound the best on that car. To answer your question we wont be offering a system for your car with the super 44's.
Thank you for contacting Flowmaster.
Nick Tauber"
"We use the super 40's in the system because we found that those mufflers preform the best and sound the best on that car. To answer your question we wont be offering a system for your car with the super 44's.
Thank you for contacting Flowmaster.
Nick Tauber"