It depends on how tall you want to go. I have Road 6 Custom 13” standard bars and fit was fine. Pull up their site and view their install on a 15 Road Glide, that will give you an idea. That video will show a couple of tie wraps to remove and a very easy move of one of the wires to have more wire play. It also depends on the bar manufacture. Seems most 13” bar are no problem, some 14” will work, some will not. The nice thing about the 18 Road Glide, the throttle by wire cable has about 18” of extra length, so no extension is needed. Also, HD went to the small plug on the throttle by wire, I think in 16 or 17, so no de-pinning is needed on any plugs.
I know this is pretty basic, but it comes down to how tall of bars and manufacturers. If you have which bars you are looking at, that would be helpful.
2018 FLTRXS, Vivid Black, KW Slicer Front Fender, Sundowner Seat/Modified by Mean City Cycle