To get some relief I built the Airfix 1/72 P-51D at the same time as this build. The masks for the transparencies were made by photographing the clear parts, importing them into Autocad where a dxf file was created by tracing over the images. The dxf file went to a Cameo vinyl cutter where masks from Tamiya sheet masking were cut. The dxf file is here if you wish to use it: http://goldeneramodel.com/mymodels/yfm1/masks.dxf . If you open the file you will see a text file, that's what an Autocad file looks like. Use saveas and save it as a dxf file.