Many boxes were painted with Hammerite (AKA Hammertone paint), so you are on the right track.
A wander through the "Vintage tool boxes of GJ will show quite a few boxes that got restored, or rejuvenated. you will also see some discussion over when to repaint, and when to simply clean and leave well enough alone.
I repainted the exterior and all the drawers of a top grade but savagely thrashed 5 drawer 50's craftsman (It's in the thread) roller, but I have yet to do more than clean the 10 drawer top box of the same era, (sort of a delema, they DON'T match, but probably should.
The roller was interesting as I had to spot weld one side of one front drawer back on, and then spot fill and sand the spot welding/repair damaged area. (hence why I had to re-paint...)
As said, no one will get rich off restoring and reselling, but for personal use and if you like the older boxes, (I do) then it can be personally rewarding, and you can learn a lot as well.