Body parts? 1984-1996 are direct swap. 1997-2001 front sheetmetal can be made to fit with some mild modification (it's been done for aesthetic reasons, although I don't care for it,) and the liftgates do not swap on either side of the 1996/1997 break.
Engine parts run a little closer - 1987-1990 will swap directly, 1991-1995 will swap among themselves, 1996-1999, and 2000-2001 will all swap around directly within brackets.
You can swap across brackets with engine parts, but it often takes a small bit of work to make things happen properly (for instance, swapping a 1991-1995 cylinder head onto 1996-up requires an adapter plate to make the exhaust ports line up, or use the earlier exhaust manifold as well. The 1996-up main bearing cap brace can be swapped onto any year of 242ci engine by bringing the studs and nuts along with - but don't transplant the caps unless you plan on having them machined to fit the new block. Things like that.)
This is exactly why I'm writing Swappology - and I'm workin' on it, guys!