One tip I picked up from doing a repaint was to make a test copy of an existing paintjob with coloured lettering added onto each section of the texture whos location and orientation I wasn't sure of.
E.g. Blue letters on one file, red on another. FFF on one part, PPP on another (use letters that are not symetrical about any axis. i.e. Not A or E etc.)

That way you can load it up and see where the letters appear, and whether they are reversed or upside down etc.
Saves the embarssment of spending ages on a cool 'F.A.S.U'' paintjob.