this seems very odd,Dom,i dont mean to be rude,but ave you assembled it all correctly?...is the disc fitted and the caliper fittd to the correct side of the new backplate?......are the calipers handed?,a good indication is where the bleed nipple is,it should be above the brake pipe fitting,please dont take offense ,but it does seem odd that the caliper is so big an intrusive to the back of the wheel,the kit was sold as 126/500 right?.
loike i say,please dont take offense.