I seem to remember Suzuki has a three cylinder engine, and rear seats split 50/50 and Vauxhall use a four cylinder engine rear seats split 60/40 and a few other changes, I know the Vauxhall had problems with the fuel tank leaking for example is was made of steel. I had the Vauxhall version and at the same time a Toyota Yaris the latter was an automatic and was my wife's, but she was in USA at the time so I alternated between the two cars, they on paper were claiming same miles per gallon, but the Yaris was much better, 45 MPG to 55 MPG on long motorway runs. I was told the Suzuki version with the three cylinder engine was far better MPG wise.
I would think it unlikely that the Suzuki and Vauxhall will have same catalytic converters as not the same engine. And you would not want to reduce the Suzuki MPG to match the Vauxhall.