That is a Gen 5.5 motor, a 5 Port going on the silver head.
This was the model before the current GX Series motors, and is a good motor.
The major differences from the GX are - TiNi coatings, lightened cooling head, and the GX carb.
The crankshaft is the same (less the TINi coating).
All the GX parts will fit straight into this engine, so spares are not a worry.
The carb on the 5.5 is sweet. Just replace the older choclate coloured needle O Rings with the new nitrile ones.