Here is a link to a page from a Chevrolet pamphlet, "Servicing Chevrolet Truck Cabs" (1947-1948), with a really decent picture of a cab with a pinstripe. Does not describe the pinstripes anywhere in the pamphlet, but from the picture, I think the stripe is larger than 1/8 inch. Also placement seems to contradict a lot of people's opinions.

http://www.pbase.com/oldchevytruck/image/93068612/original

I hope this link works, first time I have tried to do this!