My truck has a 4/6 c notch will headers and duel exhaust still work
Mine is also lowered the the same way.
I did have to cut the tailpipes behind the mufflers before they went over the axle to flip it.
I did this for a few reasons.
1st, to give myself room to work up under there.
2nd, I knew my existing pipes would interfere with the axle once it was flipped.
3rd, I will eventually be doing a motor swap and the exhaust would be getting redone anyway.
I also have lull length headers, there is no issue there. They do hang a little lower than the original manifolds did, but they are still higher than the bottom of the frame.
I'm pretty sure there is enough room between the top of the notch and bottom of the bed to sneak some exhaust pipes up and through. Just may have to notch the one bed brace under there. If and when I do mine that way, I'll probably put a little bit of header wrap on that section just to keep the heat from cooking the paint/bedliner.
Again.....you DON'T need a new fuel tank to run dual exhaust. Hopefully you saw it in my picture above, it can definitely be done. Any exhaust shop should be able to hook you up. Even if you plan on doing it yourself, it can be done.
Your choice of mufflers will matter a bit. Mine are twin turbos, but they had to mount them vertical instead of horizontal. You can see that in the pic as well.