Well, the Astra GSi radiator is mounted in a totally different position and I'm not surprised that it clashes with the trunking from the turbo to the Air Mass Meter ('J' pipe).
Mine (with LET rad) is very close, almost touching.
People do fit the XE rad with LET conversions though. It will just take a little fiddling around and you'll have to reposition it. Trial and error really but it will fit eventually.