No its not, the vauxhall z19dth turbo is similar to the 159 jtdm turbo in that it has the manifold and turbine housing in one casting but the vx turbo uses a slightly larger comp wheel and the outlet goes upwards instead of downwards in the Alfas.
I think all the 156,147 and Gt's use a seperate manifold and turbo. And the orientation of the turbine and compressor is also different, comp on the right, exhaust on the left on the Alfas as you look at it, opposite wayround on the vx and 159.