There are a few tweaks when fitting the Stretch kits. The Lower Stop Disc has to be modified – for 18″, remove the locknut, and cut off the protruding threaded part as shown above. For 20″, you will also have to shorten the hex end as well, leaving just enough to get a spanner onto.
Mudguards also need a little modification. Cut off the left mudguard stay, and just use the right stay to attach the mudguard to the slotted fitting on the fork. For the fork hook, cut off the spare bit of stay, and then fit as normal.