Someone passed this onto me via email today. Its someones auto blog and a lot of people have contributed by scanning in their collection of antique and classic advertisements as well as other things. There are 5 for the 29 Ply and many others. I know the URL seems a little odd, but there is a bunch of interesting stuff there.
http://www.lov2xlr8.no/broch1.html
Thanks for passing this on. Note the bumpers on the 29s are actually ribbed for the 28. Difficult to see hubcaps, but some look like 28 instead of the "mushroom" style for 29. Also look at location of some door handles on the flat skin instead of the raised moulding. Not all drawings can be taken as gospel.
Frank, you're right about the drawings or "artists rendition" :)