Bob, if the exhaust system is redone to dump out in front of the rears, ensure that the hot gasses won’t mix with the cooling airflow of the rear tires. I know that NASCAR (a dirty word with you) does it this way, but those cars dump the exhaust out upstream (not right in front) of the rears.
If the new exhaust system is a project that doesn’t get completed in the off-season, consider wrapping the pipes with header heat insulating tape where they pass by (and a bit upstream of) the rear bushings, if frying them is a significant problem. There might be other solutions to shield the bushings from the heat.
I too was surprised that you still had cats on the Mustang.
Second thought said that this was a hobby, not a profession… That would explain the first thought.
Third thought was “How come my hobbies’ costs would be unjustifiable as a business expense, but sorta kinda justifiable (to me) as a hobby?”
Id