The Universal Atlas of Southern NH and the Lakes Region shows Wentworth Cove Road on the left just before you get to the island bridge, so it should be the first cove north before Riley's Point. The maps that I have do not show a Wentworth Cove on them.
There were quite a few of McDude’s postcards, which showed coves or points that were not on any map either. I was hoping that someone would know about those. There must be some maps that have this information on them.
While looking around I discovered that Treasure Island is also called Red Head Island.
Sorry I do not have more to offer.
Here is an interesting site to check out.
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