Watashi no Ashinaga Ojisan

The daily lives and thoughts of the two high school girls are told through letters they write to a special someone. Oniisama e... is much darker than Daddy Long Legs, but as the main character of DLL reaches the end of high school, the tone of the series gets more dramatic. 

Both are about girls who have a hidden talent(Maya's acting talent in Glass Mask and Judy's writing). Both have a benifactor looking out for them(Masumi Hayami in Glass Mask and Jervis Pendleton in Daddy Long Legs). Both captivate the heart. 

Romances between different classes in historical settings 

Stories about girls from humble circumstances who get the opportunity to follow their dreams. Maya from Glass no Kamen wishes to become an actress while Judy from Watashi no Ashinaga Ojisan chooses to pursue writing short stories. Both protagonists have an anonymous benefactor who they meet without realizing and who later develops into a love interest. Watashi no Ashinaga Ojisan focuses more on romance and daily life occurrences while Glass no Kamen places heavy emphasis on dramatic moments. 

Both shows deal with orphan girls and gets adopted/live with/helped by other people. And both are adapted from classic books. 

Two orphan redheads and produced by the same Anime Studio. Both based on American novels. 

Both were based on the same novel and therefore have the same premise. One is a terribly short television special from 1979, while the other is a very well-made TV series from Toei Animation's "World Masterpiece Theater. 

Light-hearted and enjoyable. Art style, music and era are about similar 

Candy also gets into a sorta-Daddy Long Legs situation when the Adleys adopt her, then they both find out that their benefactors aren't exactly who they expected them to be. 

In the very last episode of Daddy Long Legs they have a little commercial for this series. The maincharacter Maria is also a lot like Judy.