If you kept your layers separate creating a bump mapping will be fairly easy:
Make a solid layer filled with RGB value: 128, 128, 128. Duplicate your rivet, panel line, and other raised/lowered detail layers, place them on that solid image and adjust their transparency to tweak how dark/light they are, merge the layer, then convert the whole thing to grayscale. You now have a functional bump map.
Follow the instructions Skuzzy lists on the forum for saving and creating the TXT file, and voila.