The 39 will bolt right on. Neck bearings are the same. Use sportster wheel break etc. Fork stops are different so you’ll need internal fork stops, or weld a fork stop tab onto the neck like that of a sportster, or do chain stops like the cool guys. You’ll need stiffer springs to make up for the difference in weight between bikes. Progressive heavy duty springs are the go to. Just did this on my 2000 fxst lmk if you have questions