If you really wanted you could "maybe" have the ball joints cut off and have them welded in.
Wouldn't recommend this though as the exhaust is 2.75" on the over axle pipes on our 5.0 and your sixxer is 2.5" so it would cut down flow some.
Be better to sell them, take a small loss and buy the correct ones.
MustangEvolution ROCKS MY SOCKS!!!