I think youll find most will fit, the problem you might have is the NSR stem, not sure if its the same on the 18 as it is on the 21 but, most here, retain the nsr stem and bearings otherwise its quite a task to get others to fit, so i think youd need to fine a good stem or a set of old yokes from an 18 first, swap the stems over and away you go, there is posts around about front end conversion, might be worth a little dig around while you wait for some more input!!