Andy, I tend to put the top of the rim on to the lamp fitting, offset and then using extended hands on each side of the rim turn the rim round until the grub screw hole underneath, lines up.
I put little arrows of masking tape on the rim and the car body where the hole needs to line up.
I hope that helps.
2011 Plus 4
Wild Mogs "Carried on to the Isle of Man" 2017
Wild Mogs "Carried on to Caramulo" 2016