I've found no similarity between my bike and a drz. The engine is completely different. I'll try to find a spec sheet and show the differences. Based on outside appearences it looks more like a yz450f motor to me.
If you go to:
http://www.gasgasmotos.es/eng/frame.htm Click on the "supermotard fsr" in the top left, and you can choose year 2004 in the top right, then at the bottom you can dowload the .pdf part list and actually look at what the internals look like.
Edit:
Model:
GasGas 450 fse
Engine
Cylinder size: 449 c.c.
Type: Monocylindric, Four stroke, DOHC, Four valves head cylinder.
Number of cylinders: One
Cooling system: Water
Bore x stroke:
95mm x 62.6mm
Injection: Magneti Marelli*. <~ Fuel injection not a carb
ignition: Integrated in injection system
Clutch: Hydraulic multi-disc.
Gearbox:
6 speeds.
Transmision: Primary with gears, secondary with chain.
Kicksart: Electric motor and auxiliary kickstart pedal.
DRZ400sm
Engine: 4-stroke, liquid-cooled, DOHC
Bore Stroke:
90.0 mm x 62.6 mm
Compression Ratio: 11.3 : 1
Fuel System:
MIKUNI BSR36, single
Lubrication: Dry sump
Ignition: Electronic ignition (CDI)
Transmission:
5-speed constant mesh