I definitely can see Kramer as being ENTP. Eccentric!
Oh and for Elaine somehow I don't see her as ISFJ. Maybe INFJ, she seems more like my mom, not really giving detailed visual information. Of course I didn't watch the show continuously as I hated, George and Newman, plus not caring much for Kramer. I know most people liked him.
Can you explain how you came to those conclusions? Especially for the main characters, and most especially Kramer.
He may be a comedian, but he's an introvert. He is not really a people-person, and he likes being around his close friends all the time. He's a sensor because he comments on real-life situations in his comedy, he's quite a practical guy. Thinker for sure, he doesn't really follow his emotions, he's a logical guy. J over P because he likes to plan his comedy routines, you see him in a few episodes working on it, he generally likes to have things done - for example, eating that lunch in a restaurant with one of his friends. He also fits the ISTJ bill far more than the ISTP one.
The I/E barrier was admittedly close, but I pick Introversion because she too gets more energized when around her close friends. She doesn't have very many friends, and she is not a people-person either, in fact the very thought of being around many people is not pleasant for her. She's a sensor, living in the present, not really the head-in-the-clouds type. Feeler because she is emotional when reacting to decisions, she is fairy sensitive and reminds me of an ISFJ that I know. Judger, she is more ISFJ than ISFP.
All I can tell is that he's extroverted, and you can tell that based on his associations among others. He's very comfortable, and somewhat talkative around even those he doesn't relate to.
Extroverted, like George, can talk a lot even around people he doesn't know. Sems to gain that nervous energy around others, even if they're not his close friends. Intuitive, he seems very unsensor-like, he's usually bumping into things, and he's sort of impractical. T over F, he doesn't seem like he makes decisions based on his feelings for others or anything like that. P for sure, he's a spontaneous wreck. ENTP is fitting for him.