Hello Leila,
I was trying to think of a good book outside of the HD manual and "101 Twin Cam Projects" is pretty good. It is well written, well illustrated, and covers everything from routine maintenance to engine mods. I'm sure you can find it on Amazon. Not to be confused with "101 Evolution projects", which is not your engine. I have a 2002 FXD i'm getting ready to tear apart. boring it to a 98" with Mikuni carb, new cams, etc, etc. I just have to finish my sporty and get it off the lift.