49mm fork installs on FXRs is pretty common. There is no 'kit'. You will have to piece together trees from one model and legs from another model. Seems complicated but is much easier than adapting a set of inverted forks from a crotch rocket.
For your FXR you probably want a set of trees without any rake, and a set of legs with mounts for two calipers. Parts are readily available on ebay, but again, you will have to source the trees and legs separately.
Best of luck.