These are part that are currently being designed. When ready they will indeed be sold through Shapeways. This is a 'test sprue' to check the quality of the designs to make sure the parts are as good as they can be. The machine-guns will eventually be sold as separate parts or included in various sets such as the turret that's currently being developped.
The engine compartment parts will be released as soon as possible. Because we do not want to guess, we are trying to get better information on various parts. We plan to make the engine set suitable for the Bronco, Heller and Trumpeter kit, which may result in several different sets.