The Pre-War side has had some USPS threads. Kind of unusual to have so many USPS threads at the same time in different forums. I would contact R McQuillan in this thread, post #11:
http://www.net54baseball.com/showthread.php?t=182497
He posts under the handle of BuyMyCard. He is a Post Master in the MN or WI region. He also is a dealer and a good, well respected collector. I am sure he will be happy to help you.
Best of luck,
Z Wheat