Yeah they should fit stright in but it is best to go and buy some autoleads apators just to be on the safe and then it save you cutting the wiring and as long as you tape each end so the connection dont come lose you should be fine then it is just a stright swap wish i had relized this before i went a brough my speakers only got 5 3/4 speakers do'h
There is a much easier of wiring the front speakers in than running wires through to the door. If you put the amp where you want it, then disconnect the ISO plug for the speaker leads.
Take your wiring harness for your HU and cut the speaker wires in half. Then wire the leads from the amp into the ISO plug side of the wires, obviously getting all the colours correct. Then just plug the ISO back into the Corsa wiring loom and use the original Corsa wires to get throught the doors to the speakers.
Sounds complicated but much better than drilling wholes and having loose wires. It worked for me anyway.
Just remeber to seal off the speaker wires from the HU or it will go a bit wrong!! 8)