Okay there's a big diff between SVS and SVS STYLE headers as far as fit. I'll give you the general quick run down. Use ONLY new factory DODGE header gaskets, if they are'nt SVS you may have a problem, but let's assume they are SVS. Make sure all flange surfaces are smooth and flat. Install each tube finger tight or just slightly loose. Look at the tubes where the collector will slip on. They should all be within the same plane, make sure none of them are hitting the frame or any thing else. A note here, starting with new motor mounts is a very smart idea. Okay if everything looks great, try to carefully slip on the collector. Make sure you have no clearance issues. At this point your likely to have some axial misalignment with the rest of your exhaust. If your anal like me you'll start cutting and welding to get everything perfect (Heliarc comes in real handy for this job).
Chances are your going to need Quick fire oxygen sensors if you've got a later model Gen II. DC Performance has these, you'll also need some heat shielding for the oxygen sensor wires and likely some extenders for the wireing harness on the 02 sensors as well. By the way make sure the car is up in the air SAFELY when your doing all this stuff. You might want high flow cats as well as V-band connectors or some other form of connection for the post header joints.
Oh I almost forgot, the OEM shields won't work for this application, so either you get some ceramic sleeving (budget method) or you spring for some $700 inconel shields. Let's not forget about the plug wires as well, if you are'nt super careful you will smoke some of them as well. If you think you don't need shielding with the SVS headers, price out a new or used heater (blower motor) enclousure. You'll be ordering one shortly thereafter. Good Luck
If you can figure out how to get in my photo gallery, I've got a bunch of various picks going through this procedure.