Apologies if this is well-known (especially on this board), but Marty got its start as a Paddy Chayefsky teleplay with Rod Steiger and Nancy Marchand, later of the Sopranos. The movie with Borgnine and Betsy Blair came out a couple of years later.

Betsy Blair was Hollywood homely, which meant she could reach down to play as "pretty but plain" (even then, she had killer pretty eyes). Nancy Marchand, well, may have been more suited to the role:



For one thing, she was bigger than Steiger.