The clean and scan thing is done with multiple scans and reassembled in photoshop, normally done to preserve the art before it gets all messed up with bondo. Not real important with that one however there are a few good reference copys already available.... You will run into some problems with your plan however, That art was originally a screenprint on wood, that's not going to be reproduced commercially like ever (more likely than not) and after fixing that cab that art will be trashed.... So 3 options, the first (and what Jenn does) paint the cab sunburst yellow and slap a sticker over it, #2 airbrushing, a very time
consuming and expensive approach, or Make a screen set (or stencils)... Be careful who you talk to with that last one, That cab has some very protected copyrights on it.... And FWIW, the "T" moldings on that cab was orange originally, somebody changed that one.