Theres a few options....
Banks makes one IIRC
Get a Powerstroke 3" one...have your stock end welded on and fitted...
Modify the stock outlet to fit a 3" PS and get a Vband adapter to weld to the stock outlet....
There are tech articles on these methods....I think simplest is 3" PS dp and add the stock 2 1/2" Vband to that pipe...adapt the two together...only welding thin wall pipe not the cast...
hope this helps