I have made a mistake. I wanted to purchase the 25mm plenum spacer to suit an ecotec, instead of the 12mm version. Could I just pay the extra into your paypal and organise this ASAP?

If you have a boosted ecotec then we would recommend going with the 25mm plenum spacer. If this is the case then we'll organise a paypal invoice such that you can make payment for the difference. Otherwise we would recommend sticking with the 12mm plenum spacer which you've purchased.