Engine bay, door jams, under hood and deck lid, along with the wiper cowl as well. If you’re going back to the original color? Maybe it ain’t necessary. If you’re changing color? Absolutely necessary.the big issue, to me, is that to really do it right, you need to paint the engine compartment to match the rest of the car, nothing says "repaint" on a mustang than a different color engine bay. So that would just make the cost astronomical, It would suggest, and as many people have said, look at a wrap. I'm not a big fan of those in general, but they hold up pretty well (our Porsche GT2 was a wrap). The best thing is, you keep the stock paint jog underneath which will add value to the car, rather than a repaint, which is not only expensive, but devalues the car.