Hi Nomada,not many M100 cars in NZ ,eh!.
Actually there is a ton of difference between the Euro M100 and the US spec engine,all resulting in a blunting of the sheer grunt of the best engine ever built.
(if you think your chev,ford ,ferrari etc engines are better ,why are you here ?)
The main difference is the low compression of the US spec engine.Low compression gives lower combustion temps,thus lower N0X emissions.allowing californians to breathe better .but at a slower pace than europeans [:D]
This low compression is attained by dished pistons,the combustion chamber is same size as are the valves.
The cams are different,I don't have the US/euro differences to hand but the US cams were milder ,again to lower the emissions through different exhaust timing.
Ignition distributors are also vastly different,the timing being later in the advance.
If you want to get more Horsepower ,(god only knows why?)Pistons will cost a grand a peice,cams are almost impossible to buy second hand so new cams,valve springs and hydraulic adjustors are required ,thats about $5000.
Have you changed the timing chain ?.Do that first,then get the fuel filter changed,followed by an ultrasonic clean of the injectors,then see if still need to upgrade the Horsepower.
This a pic of Phil O'briens TURBO 6.9 ...something to ponder.