I have done this on newer k5 bikes, as I recall the steering stem on the 88-89 bikes is to small on the bottom where it presses into the clamp. I ordered a newer stem from emig racing. If I were going to all the trouble I would try to get a set of 05-06 kx250 forks or at least a set of 04kx250f forks. A couple of years ago I picked up a brand new set of 250f forks on ebay for $250, and recently got forks and shock for $110. I'm sure there will be some response that the k5 forks are as good as the 250 forks, but, having raced 125, 250f and 250 for many years, I can tell you the newer stuff is much more advanced. If all you want to do is trail ride then maybe the older stuff is OK, for my money I try to go with the latest stuff. I have 2 k5's in 02 kx 250 chassis and 1 in a 04 250f chassis (work in progress) 2 have the o4 250f forks and 1 has the 02 250 forks they both work good. 1 other point the 99-01 125 and 250 forks are the same, they have different valving and springs. the 02 forks are larger diameter so iff you change make sure you use the forks and triple clamps from the same year. Good luck.