It has been said before but i'll repeat it. You CANNOT SAFELY rebuild/reline/restore and old helmet.
If you want a piece of period costume to look cool with your bike at a static display, that's fine. Go right ahead, but what you'll have on your head is not a helmet. It's a piece of costume. Let's keep that in mind.
I understand that many peeps on this forum think that this is ALL about the look, and sure, looking cool can be fun, but this is way more important than looking cool. Go visit a rehab center and look at teh bikers who were cool and didn't need to wear a helmet because they were too cool.
Helmets deteriorate over time, and offer little or no protection. Pudding basin types provide no coverage for your face or temple area and are basically useless in most accident situations.
I am totally uninterested in any arguments about it being your choice to make a veggie out of yourself or your rights as an American to be dumb. Sure you have that right to act like an anti social moron, but you also have a responsibility to take care of yourself and not leave the rest of us to have to deal with the consequences of your actions. Just because we have a right to do something doesn't mean we should. We have the right and responsibility to do what makes sense.
Does that mean that we should do nothing that has any risk? Of course not. We have choices. We should use them wisely. using an old helmet on the street is not a wise choice.
That's my opinion. Yours may vary.