Building a W engine is something you will have to want to do because you want that engine in your car for a long term deal,its not something you can do thinking you can flip it and make money off it if your project changes direction.While they are harder to find and desirable,those same traits make the missing parts harder to find and more expensive,the normal rebuild parts are little more expensive to boot.Unless you can get the cores for a smoking deal and can do a lot of the work yourself or get a machine shop you trust that has really reasonable rates,the cost of building the engine can easily equal any potential selling price.