[Unobtainium]

Headers on a s/c car are not great value. At or near stock power levels, the gains are minimal vs cost. A pulley change is way cheaper and easier. The GT500's have gone through the same thing for years. I've seen very little gain until they are wound-up pretty good, like 600whp good. Then, you see about 20-30whp over factory manifolds. The big benefit is that they lower boost for the same power, and sound better.