alot of kyb's are just stock replacement. willie runs them, im sure he will chime in and give you the lowdown.
The non-adjustable gr-2's are OEM replacements and can be used with stock springs or can be used with lowering springs like Eibach Pros. If you want something stiffer or adjustable you want the AGX's, however those aren't as straight forward as far as replacement goes - requires converting the stock sealed rear strut tubes to accept a cartridge like the fronts. There's lots of posts about the conversion if you browse or search the site.
