A quick look at the files for the default DC3 in FSX looks like they may convert fairly easily. M$ have done a bloody infuriating thing by flipping the main texture file so that it's inverted. I think that is a change just for changes sake as there seems no other reason to do it other than to bugger people about. There are night time textures in there as well which I don't have so not sure how that will work if I just omit them. I'll have a tinker with them and let you know.
Edit: I've copied a texture folder in the FSX airplanes DC3 folder and dumped one of my repaint textures in there. I've tried to convert the texture using DXTBmp and all the DDS format options result in a transparent aircraft. I downloaded a small utility called ConVim which gives an option to save as DDS DXT1 and I got a partial success. The texture looks like its in about the right place but the quality is awful.