"toms94" is correct. On an L98 the advantages of "shorty" headers over stock manifolds is dubious, however, you can spend nearly the same money for a lower restriction exhaust after the cat and gain something.
Now, "long tube" headers can be an advantage, however, the improvement on a stock or near stock engine won't be great.
Where the long tubes will become valuable is after you do other mods such as changing the camshaft, the intake manifold, runners and plenum and porting the heads.