I used to have that same combination.  I cannot think of anything short of a couple of custom made pipes to hook it up.  If you are doing it from scratch, consider getting some of those ball/socket connectors.  Those headers tend to bend the flanges on every speed bump you encounter.  The ball/socket setup gives  more ground clearance plus doesn't leak like 3-bolt flanges.  They make them in 3"x2-1/2" or 3" x 2" or 3" x 3" so the transitionin size from header to pipe is done in the connector.

Flowmaster Ball Flange Kits 15925 from Summit Racing.  Walker also has same thing for about 1/3 price.  You cut off the three-bolt flange from the headers and weld this on, then weld the pipe to the other section of it.  Goes from 3" header to 2.5" pipe.  They also have other sizes if that is not what you have.

This is the only way to go...

Why do you need an S bend?  Mine went pretty much straight back with some mild bends to clear the crossmember and floors?  The DO sell them if you go to SUMMIT or JEGS catalogs online, though, if that is what you need.  They sell J bends, S bends, probably XYZ bends if you look.

Here is an old trick to avoid having to take your car to a muffler shop to get a couple of pieces made:  Buy a stick of 3/16" brake tubing.  Bend it to fit where you think the centerline of the pipe you want will need to be.  Cut it to the right length.  Once you get it bent to fit where you think the pipe should go, take it to a muffler shop (the tubing, not the car) and tell them to duplicate it in the size tubing you want.  They can weld the fittings on it, flare it or stretch it so it fits over another pipe as you need.  And it won't cost alot.  I would rather make 2 to 3 trips to a muffler shop fine tuning a bent piece of pipe than having to tow a car over there once.

GPatrick wrote:

Hey David, if you need tight curves you may want to cut the H-pipe section back a ways to make the transition smoother.  I don't know that setup but is the H fixed or is the center a slip joint?  If it is a slip, you can slide it apart a little to spread the pipes up front or you could cut the H  and make it a slip joint pretty easily or even weld it back up after you figure out what space you need to add.  I like the wire idea - especially since my brain doesn't work very well in three dimensions - add that to working upside down under the car and an easy pipe transition often looks more complicated than it is.  Also hadn't considered having the shop just make the parts.  The last time the Mustang needed exhaust I drove there with open headers!

 
Hey Gary. The H pipe is welded and doesn't have a slip joint unfortunately. I'm gonna see what the local muffler guy comes up with and will let everyone know. Thanks.