Do the mustangs use the Flowmasters? If so which ones do they use and are they avaliable in a SIDO?

 

Flowmasters, yes.
SIDO, no.

They have true duals and headers from the factory (85-current I think)

I had a mandrel bent BBK 2.5" "H" pipe with only two cats, offset 2.5" FloPro mufflers (straight thru design, no packing material like the Dynamax) and 2.5" mandrel bent tailpipes on my '86 5.0 GT.

Very loud and I loved it. Wish I coulda kept it, but economics would not allow it and the F-150 in the same garage