Epoxy / Bondo?
You can try using some sort of tape applied to the inside so it follows the shape of the body and then some Bondo or 2-part epoxy applied on top of the tape, troweled even with the outer surface of the body. After it dries, you'll have to sand it smooth (when in doubt, use a higher number sand paper). Wet sanding may be good too. When its all done, you can paint the body high-gloss black. I wouldn't worry about damaging the NE body too much. Unless you can patch it up, it would likely be suitable only for parts.
As for your 302, you must do 2 things.
First: NEVER let your dad near old stuff again! He can break all the new stuff from Wal Mart he wants, just leave the old stuff alone!
Second: try wet-sanding the body with progressively higher-number sandpaper BY HAND! By hand is important because the random strokes of your hand will not leave the streaks of a machine. You can also try using automotive rubbing compound then automotive polishing compound, both available at your local autoparts store.
Tackle the Northern Electric phone first. If you are successful in patching and painting it, you might try the same on the WE-302. Just be sure to put some good use on the NE phone first to make sure it sticks. You may need to adhere some nylon window screen material across the back side of the holes and cracks you are patching to give the epoxy material a better surface to which it can stick.
Good luck,
Dave