Astra looks like a very tidy conversion!
I remember there was a rover 25 at combe a couple of years back, it had a v6 in it (out of rover 45 / 75 maybe?) at was all on the piss in the engine bay, driveshaft angles were all over the place, it looked like a pissed up cow sat in the engine bay!
I think if you spend some time fitting it properly getting everything right then it could be a good conversion, but just lob it in and it will ruin the car.
Although, seeing as a 2.0 zetec will pretty much keep up with one it just seems not really that worthwile to do, especially as the zetec is a much stronger engine and has a bigger tuning potential.