After I sandblasted the heavily rusted grill pieces of my '48 Stude pickup to a 'metal in white' condition, the areas between the grill bars were deeply pitted after all the visible rust had been removed, some pits penetrated almost 2/3rds of the way through the metal. (nice M-5 grills are very hard to find- and quite expensive)
Having had previous experience with the toughness of a well applied coating of POR, I figured it would be ideal for this application, as it is extremely resistant to chipping. I applied 2 coats and let it harden completely, then sanded them lightly and filled all the pits with fiberglass resin, sanded, and laid on 2 more coats of POR, at this point the parts appeared as new. I intend to scuff them one last time and spray them with J.D. 'Blitz Black'.
The point of this post is about economics, practicality, and durability. These parts had survived over 50 years with the minimal protection of the factory applied paint. (this was a working farm truck, so it likely never even received so much as a single wax job.)
Several times it has been suggested in this thread that the 'cure' for rust is to just "cut it out, and replace it with new metal"
I'm here to tell ya that just isn't practical advice when dealing with parts as intricate as these grille pieces, IF it could be done, (it would take one hell of a skilled metal-worker and a lot of hours) the labor cost alone would run into the thousands.
And after all that labor and expense what have you got but a grill that at its best is no better nor durable than the original.
Which brings us to the subject of durability, This time around it is reasonable to expect that the vehicle will receive better care than it did formerly, (if not it would be rather pointless to even begin a restoration.)
There is every reason to expect that the restored parts, using modern tech. coatings and paints, and TLC will last far longer than the original factory applied finish, which in this case is another 50+ years.
I would expect this to be true wether POR-15, or Epoxy primer/ paint systems are employed.