Does anyone know if the twin cam engine and trans from a 2003 Road King will bolt into my 1998 FLHTCUI?

 

It will but you will have to lower the rear under-frame cross over or make a custom oil pan. Also IIRC on some of the evos you need to change or modify the front break master cylinder location. John Kitzmiller of Zippers Performance did an Evo.. I've done an after market FXR evo frame an only had to lower the rear cross over.

 

Don't forget about the ignition too. Evo's have the cam cover, TC's use the crank position sensor (from those respective years, anyway).

And you typed in FLHTCUI, which implies to me MM fuel injection. If the Road King motor is FI, that's the Delphi system.