I'm designing a plane from scratch right now and I'm using AutoCAD 2004. I wish more people had access to it, but there are many other CAD programs out there you can use just as well for what you are describing. My plan is coming together nicely. I figured out how I wanted the thing to look and started picking points.
In your case, I would say scanning is the way to go. While you are at it, get a copy made first, then setup some reference points on the copy so you don't mess up your original plans. The hardest part about CAD is picking points if you don't know where they are. The more detailed the part you are drawing, the more points you will have to pick. Curves are diabolical... Trim, Extend, Offset, Move, Rotate and Mirror are your friend. Learn them and use them. They will same you more time then any other commands. OSNAPS are equally good and bad. Get used to turning them on and off. You'll find you want to leave about three or four of them on almost all the time, but there will always be an occasion where you'll only want one to be on. Layers are also your friend. Use them all the time. I have a layer for each group of things I'm working on (i.e., Ribs, Leading Edge, Flaps, Ailerons...) which lets me hide these parts to make viewing and drawing much easier. You should also like either beer or coffee. Beer or coffee makes everything better, in moderation of course.