The idea of the OVA is based off of "Romance Dawn: Version 1" which was one of the two prototype manga that were made from 1996-1997. Way before the actual One Piece manga was created.
This is the first One Piece anime to ever show Gold Roger's eyes.
Silk was Oda's first attempt at designing a Nami-like character. She shares much of Nami's personality, however was much more kind and seemed to boast more leadership skills rather then relying on force to make people do things. Appearance wise, aside from her hair being long everything about her (including her choice style of clothing) was almost identical to Nami.
Several fight scenes are closely matched to original scenes in the first "We Are!" opening, particularly, Zoro and Sanji's respect scenes.