I have built a couple of FLST's using the DNA rear and swingarm. As these both have bodies, I used a set of true dual pipes from Samson. From where they end, you'll have to get your muffler shop to make up two "S" bends out of 1-3/4" pipe, then what ever muffler suits your fancy and length. For hangars, you can use a piece of "U" channel, bolting it to the frame and mufflers.
If the trike has an open rear, you can use V&H shorties, as well as others.
UB