PSA grades JD McCarthy postcards. Below is a link to a Mantle that is offered for sale now (not mine):
http://www.ebay.com/itm/1960-70-J-D-...item258a5124e9
My understanding is that the year on these varied and that he continued to produce them through the 1970s. As a result, they do not necessarily bring much. The best way to date them is to find one without a zip code or do like Adam and look for ones with postal use, which is my preference as well.
It's a very nice card. Regardless of the price or year, I hope you enjoy it.