The pole appears to be the factory pole for a 6' Sinclair HC sign. I don't have ready access to one to measure and see if that sign is indeed 75" as opposed to 72", but it is definately a Sinclair pole. One of the photos shows two poles, including one of the later Sinclair frames with a "fitter" base that fit on top of the same type of HC pole, a logical progression as Sinclair stations that used porcelain signs would have progressed from the HC (supposed 6') to the later Dino sign.
Hope this helps.
Petroleum Collectibles Monthly