Show That Lowered A-body!
Doug's headers provide almost another 1/2" of ground clearance vs the TTI long tube headers from what I understand. On my Duster the Doug's are sitting a little less than 4" off the ground. That's with 25.6" tall tires and the wheel openings just under 25" off the ground.
TTI shorty's would be the next step, that would get you the same clearance as a set of manifolds.
This is the passenger side on my car, the passenger header hangs down a little lower than the driver's side. You can see that the flanges are pretty darn close to the floor pan, you really can't tuck them up a whole lot more than this if the flanges are anywhere near the same spot. The frame is only 6" off the ground there, which is at the back of the torque box. The skid plate on the K member was only 5.5" off the ground here. I've lowered the car another 1/4" or so since I took these, so figure 3.75" to the header flange, 5.75" to the frame, and 5.25" to the skid plate on the K. I still haven't dragged the header flanges on anything. I'm still running the stock LCA's with a 3/8" tall poly bumpstop, and have about 1" from the bumpstop to the frame.
Car as it sits now. I'm running out of clearance on the fender lip when turning, but the plan is to roll the fenders and drop it another 1/4" or so in the front and maybe another 1/2" in the back. Based on my experience with my Challenger that will put it to where I need to be pretty careful with the local speedbumps to keep from dragging the the passenger side header flange, the magic number for most of the places I drive around here is pretty close to 3.5" of ground clearance at the flanges.