GENII's had cast iron manifolds in 1996 & 1997.
As Marv states, in 1998 ~ 2002 Dodge went with 23lbs lighter (combined) stainless tubular manifolds.
They require not only the 1998 ~ 2002 turn pipe / cat combo, but new (shorter) manifold bolts and studs along with 1998 ~ 2002 heat sheilds and new style gaskets.
I made the switch (too cheap to pay for headers) and found that yes they are indeed 23lbs. lighter. Beyond that, a waste of time and effort.
The newer manifolds increased the side sill temps as the cast manifolds acted as a heat sink. Was the reason why Dodge went with them, quicker cat light off on cold start.
They added zero horsepower. I dyno'd SAE corrected, same dyno, 435.1 RWHP with original and 434.9 RWHP with the new style. If you were to closely examine the cast and tube manifolds, you would suspect that the cast actually flow better given the sharp bends and frame clearance dents in the tubes as Bruce mentioned above. I have plenty of pictures available if anyone cares.
Save your time and money and stay stock, or if you have the mod itch do it right and step up to real headers.