Visual Basic or C# with the Visual Studio forms editor seems like the fastest solution, assuming Windows only. There are multiple ways to approach this program, but this is what I would do:
Create a Data object that stores all of the settings (size, material, etc.)
Create a Render method that renders the print according to the settings data (draws the print as background, draws values of dimensions and material properties on top)
Create a Form to use as the editor. The form could have drop down menus for preset options, or numeric fields that can be modified. The form binds this data to a Data object, and saves/loads the data object using any standard serialization (xml, binary, etc.).
With this setup, you can meet all the requirements, with the possible exception of editing the actual print, but you were a little vague with that.
Now as a mechanical engineer, I have a possibly different idea of what he wants, and perhaps you should ask him about this. The drawings you posted are obviously from CAD software, and the idea here is that instead of having to model each individual part in a series, you just want to be able to tweak the dimensions quickly. Now if you have the CAD software, this can be done really easily in no time at all. If you don't have the software, however, this is impossible. Thus, this leads me to believe that the intent of this program is to allow customers to specify a new custom part that they need, without having access to CAD software. If this is the case, he should just find a browser-based CAD application, as there are many existing ones that are free or are available for a small price. Then he could post the drawings in a standard format and any potential customer could edit the dimensions to their liking.