Posted By:
LymanPhil, thanks for your interest. Issue #8 of Old Cardboard magazine (which includes Jerry Spillman's 6-page article in full color) can be obtained at http://www.oldcardboard.com/subscriptions.asp. The article addresses you question in detail and provides insight about the W600 set never before published.
While you are on the website, you may want to consider a subscripiton to Old Cardboard. With questions like yours, I have no doubt that your subscription will pay for itself many times over. Your support is also much appreciated and allows us to continue to serve the vintage hobby with a full color magazine.
That is my humble (and totally unbiased) opinion.
Happy Collecting,
Lyman (editor@oldcardboard.com)