Here's a few screen shots of the Panhead engine for one of the choppers. Not all the detail is there, but that doesnt really matter since it will mostly be a blur going across the screen anyway.
For my modeling and rendering I use Maya. Its not necessarily a "CAD" program. What I mean it's not like an engineering program where you enter a lot of numbers. There are a few places you can, but for the most part working in Maya is like sculpting clay.
To model this engine, I just followed the blueprints for the basic shape and a number of reference photos.