Did you know that Philip Burns who played Fred & Lamonts goofy accountant Calvin was on Seinfeld He played Jerrys dad Morty Seinfeld in a few early episodes

Yes, although he really wasn't any good on Seinfeld.

Yeah they let Jerry and Liz Sheridan who played his mom have most of the lines. I remember him basically having a few lines about Jerry's taste in women and Loni Anderson basically was the straight man for Liz Sheridan

He actually only was on Seinfeld once. Same thing happened with George's father. The first time he was played by John Randolph, then they replaced him with Jerry Stiller. They actually reshot the scenes with John Randolph when it went into syndication, but too much time had passed for them to reshoot the scenes that had Philip Bruns in them to make it work.