1. Do you know of any sites that sell weather stripping for these cars?
***No company that I am aware of makes stock replacement weather stripping for this vehicle. Either you use the generic weather stripping sold at your local parts store, or you may check metrogasket. Com***
2. Do you know of any sites that sell complete performance or o.E.M. Catback systems for this car?
***Any performance parts for this vehicle will have to be special-ordered***
3. Do you know if a header for a 300zx 3.0L would fit properly in a 200sx 3.0L?
***While they had the same engine (VG30E used in 300ZX until 1989), the exhaust pipe is different (based on Maremont website) between the the two cars. I believe the header may fit (with some modification) but you will have to modify the pipe quite a bit.***