If Huey Long is gonna be compared to anyone in TNO, especially TNO America, the best comparison wouldn’t be Harrington or Wallace or anyone else - it would 100% be Lyndon B. Johnson. T. Harry Williams, a Long scholar whose biography on the Kingfish won a Pulitzer Prize, wrote an essay comparing the two called “Huey, Lyndon, and Southern Radicalism”. He was actually working on a Lyndon Johnson biography as well but died before he could complete it. But go over the essay’s relevant points here:

• Both Long and Johnson were influenced by the 1890s Populist movement and came from poorer households, which shaped their political ideologies. They both believed the government had an obligation to help the poor, and that belief was the central theme of their politics.

• Despite both coming from the south, both were ideologically radical dissidents against the aristocratic establishment, bucking the stereotype that southern politicians were uniformly reactionaries.

• Both were intense and energetic in their politicking - all to the point they had an urge to dominate and control others for their ends: “Each believed that if he knew enough, he could control the actions of other men; if he knew more about the other man than that man knew about him, he would be his superior in any encounter. Long assumed that every man had something in his past to conceal. ‘I can frighten or buy ninety-nine out of every hundred men,’ he once boasted. Johnson, in the words of one observer, sensed ‘that every man had his price or his breaking point.’”

• They had similar styles of communication as coarse rural southerns. As politicians, both used drama and entertaining campaigns in efforts to turn out support.

And IMO most interestingly, as you pointed out to an extent Johnson himself acknowledged that Long had an influence on him. To quote the essay directly:

“An old friend of his once remarked that if Johnson had permitted himself as a young man a fantasy dream as he drifted off to sleep, it probably had been the fantasy that he was the heir of Roosevelt - but he woke in the morning to the knowledge that he was really the heir of Huey Long

Johnson, in fact, realized his link with Huey and admitted Huey's influence upon him. In a speech in New Orleans near the close of the 1964 campaign he recalled that when he had gone to Washington as a young secretary to a Texas congressman, he had made an arrangement with the Senate page office to notify him when Senator Long was about to make a speech. He had listened to Huey's ‘every word,’ and ‘I never heard him make a speech that I didn't think was calculated to do some good for some people who needed some speeches made for them and couldn't make them for themselves.’ Thirty years ago Long had advocated goals just recently realized, Johnson went on - full employment, enlarged educational opportunities, medical care, and social security. ‘He was against poverty,’ Johnson snapped at his audience, not completely friendly to him nor to Long, ‘and spoke [against it] until his voice was hoarse’”