XJ40 Tyres

[KG7]

I have a 1988 XJ40 3.6 with original alloys and metric tyres. I have been offered a set of XK8 alloys with 255/45/18 tyres. I have seen various photos on the web of other XJ40's with these wheels and tyre combination. Is it likely these tyres will foul the wheel arch ? and if so is the modification to the wheel arch difficult ? Maybe the only way to find out is to fit them and give the car a run but any info out there gratefully accepted.