Difference with headders are:
- "Long" headders without primary catalytic converter; Eu and Saudi cars.
- "short" headders with double catalytic converters; USA, Sweden, Switzerland.
So basicly high emsision and low emission versions. also ECU have different mapping because of this.
difference is also in heatshield, if you EU cars do not have metal plate next to primary converters.
I also have this speculation about catalytic converter issues early cars suffered. Thing is if you got original converters they will go bad and actually blow back depree to engine and cause damage and this is real issue. But I think this is more of issue for cars with primary converters, because timing and valve opening with collapsed secondary converters would flush exhaust towards some odd cylinder and wash away depree from primary catalytic converters, but this is my theory (yes both converters in my cars where collapsed inside, they all are)