I doubt that fully dimensioned CAD drawings are available for many of our engines or accessories, as it would make duplication too easy. What I have done for drawing plans and determining fit is to capture a bitmap image, then convert to vector using Adobe Illustrator (trace). Many of the engine manufacturers offer three-view or at least front and side view images. Of course, getting the proper scale can be an issue, but all you need is one dimension, and everything else should be proportional. Since the mounting dimensions are most important, I usually use them. Beware, you will find distortions even in the manufacturers' images. John