On one of the LITB Facebook pages some years ago, someone recalled how, back when LITB was in its initial run, audiences in a particular area of Ohio recognized some of the character names as belonging to real people from that locality: Larry Mondello, Miss Landers, etc. And Eddie Haskell was based on a friend of one of Connelly's or Mosher's children (his name was not really Eddie Haskell; he had an Italian name).

Makes me wonder whether most if not all the names on LITB were taken from actual persons. Cleaver, Beaver, Wally, Ward. These don't necessarily sound like generic screenplay names. Larry Mondello certainly doesn't. Names on other period sitcoms were more generic (Jim and Margaret Anderson, Betty, Kathy). Were the LITB characters based on real people the writers knew? Perhaps we'll never know, but I have a hunch they might have been.

You're right -- we'll probably never know how the main cast names were chosen.

Other names such as Mondello, Rickover, and Hensler certainly are uncommon. Two of them are flagged by spell check.

For names that are only mentioned, or are one-shot or infrequent characters, they picked and frequently used two sort-of common names: Henderson and Thompson.

I was curious to see if spell-check would flag any of the other surnames of recurring characters from the series; none that I found:

Anderson
Bates
Bronson
Brown
Canfield
Dennison
Foster
Fredericks
Rayburn
Rogers
Rutherford
Whitney
Woods

Apple's spell check flagged Mondello and Hensler. I don't know if all brands use the same one though.

It reminds me of the names in "Peanuts." Charles Schulz based many of the "Peanuts" characters on people he knew. There really was a Charlie Brown, an art instructor in Minnesota. Likewise Linus Van Pelt and many of the other names were drawn from real life.
Snoopy was based on his childhood dog, Spike.