The 2.2 JTS is a significantly re-engineered version of the 2.2 opel Z22SE/L61 engine. They indeed share an all aluminium block and crankshaft. The twin balancer shafts which are also shared, reduce 2nd order vibrations (providing the 2.2JTS its v6 like smoothness) but add weight while introducing a power penalty. It's a pretty decent 4 cyclinder block to base an engine on.
That's where the similarities end, the head is completely different and adds variable valve timing (the twin phaser technology) and Alfa's JTS direct inject. Vauxhall owners have in the past inquired about retrofitting alfa parts to transform their 2.2's into a 2.2JTS. But it's no dice I'm afraid, the engine is significantly different and nearly all parts are not interchangeable. But hey it's good to see the Vauxhall owners aspiring to the JTS engine.