Can you buy one header?

I would give up 25 HP for increased ground clearance about as quick as you can blink an eye. Trying to get every ounce of power out of a street car is senseless when you could have something nice to drive everyday and not have to worry about knocking your headers off or spending 800 dollars on a set of long tubes. Do what you want.

the other opion is to just do the right thing and crank up the torsionbars or install taller tires so the car gets back to its intended rideheight and the problem is gone forever and with a set of headers you will gain not only those 25 hp you will more noticeable find a bunch of torque at low rpm that is worth everything on the street.