"will look shit, trust me !!!"
Personal taste, lets not forget that HZ GTS's are not Monaros....
If you want to be different get a c/f or fibreglass rear boot which is moulded to be level with the 1/4 panels, they look good. If not then just weld the holes, fill the "slots" where the original wing went and have a smooth lid. Its all personal choice,