If you have EGR, blocking the exhaust port may throw a code. My 91 hatch does not have EGR. Blocking the exhaust port, with my header, is a non issue.
Header benefits, on a G10, is debatable. The stock exhaust manifold is pretty much a header design to begin with. Nice aftermarket converters are available from Summit, Jeggs, etc.
.........I'll be back in a bit........Extreme Make Over....SnowFish Addiction
1991 Metro Xfi Sport, Crower F12142 Cam, +2 degrees on adjustable sprocket, .020 Over, Balanced & Blue Printed, 3.79 final drive, WhiteLine Bushings Everywhere, 185/60R14's, TBI Bridge Delete, Edelbrock Air Cleaner, Stainless Header, 2 Inch Exhaust, Magnaflow GlassPack, Swift Twin Exit Muffler.