the racks are not to bad to change if i remember rightly remove downpipe and disconnect gear linkage and then lower rear of subframe (doesnt have to be completely removed) .basically remove rear and middle subframe bolts and undo front bolts a little just so subframe lowers enough to slide rack out of drivers side ,also remove roll bar links and your pas pipes .we used to use a decent transmission jack to lower the rear of the subframe obviously safety is important .
hope this helps i may have forgotten something but that is the jist of it my vauxhall main dealer have been over for a while now