What does “a Kosher ham” signify in the line, “Stone described himself as a kosher ham ready to go to the opening of door.”?

a kosher ham ready to go to the opening of a door,

I. F. (Izzy) Stone was born to Russian Jewish immigrants who named him Isidor Feinstein. According to Wikipedia:

On the advice of an editor that his political writings would be better received if he were not perceived as Jewish, he changed his name to I. F. Stone in 1937. He would later recall he "still felt badly" about the change, and referred to himself as "Izzy" throughout his career. [Emphasis added]

Kosher Ham seems to be a Jewish joke played on Gentiles, who don't understand that pork cannot be kosher, regardless of the curing process:

For no reason whatever, I decided then and there to ask the deli lady, "Is this kosher ham?" Instead of the scornful laugh I was expecting, her response was, "I don't know, I don't buy the meat..." I said nothing in response, having been rendered speechless by such crass ignorance. I thought of it as a fluke. Surely the vast majority of people out there knew better! ... Wrong!!

I decided to try this again about ten years ago... Sure enough, when I asked the young lady if they used kosher ham, she picked up a pre-made sandwich, began to study the label closely . . . until I let her in on the "secret." Couldn't believe it.

Since then I have repeatedly "gotten away with" this joke, with people I thought surely would know that it was, indeed, a joke.

Apparently, when I. F. Stone, called himself a kosher ham, he was poking fun at the social conundrum of his life:

He was happy to fit into a Christian culture. He had even changed his name to make himself more acceptable. But he understood being Jewish remained an obstacle in his social networking.

In the expression, kosher is analogous to being Jewish, while ham is analogous to fitting in with a Christian culture. His response to the author's special invitation demonstrated the modus operandi of his life. If a social door was opened to him, he would gladly enter.

A ham (originally applied to actors) is an old, low-quality entertainer, so Stone may have been self-deprecatingly describing himself as, though not good, professional enough to take on any paying project. In favour of this interpretation is that "ready to go to the opening of a door [in Britain often the opening of an envelope]" is often applied to minor celebrities who will attend any function (such as an 'opening night') where there wil be publicity and free champagne. Against it is that 'hack' would have been better than 'ham'; but then you couldn't have the joke about kosher ham.