You mean the Libra's own oval 'splitter' that feeds air to the radiator rather than any aftermarket part I believe.
I seem to recall having the same head scratch moment when I did this bit - it's not actually catching where you think it is.
You need to trim back the front lip of the radiator duct to allow the lower inner lip of the splitter to pass it as it goes down past when you open the bonnet. With the bonnet shut and the splitter held in place there should be a gap of few mms between the inner bottom back edge of the splitter and the front lip of the rad duct.
Attachment:
Libra splitter rad duct trim.png
FYI The bottom flat bit of the splitter goes under the rad duct and should not need trimming IIRC.
SAS