What records are available for the Delaware Native American Tribe (Lenni Lenape) in Eastern PA and NJ and who might help with this line?
A good place to start with Native American research is the FamilySearch.org Research Wiki. All you need to do to get started is to type in a subject such as “Delaware Indians” into the search box. Here is a screenshot of the startup page showing the location of the search box with an arrow:
When you get the response, you will see that there is an article on the Delaware Indians. You can then click on the name of the article to go directly to that article in the Research Wiki. As you have noted, the Delaware Indians were originally known as the Lenape or Lenni Lenape Indians, the name they called themselves. The American colonists named them the Delaware Indians.
You should know that many family traditions asserting that an ancestor was a Native American are disproven. So the best way to begin is to carefully document the line with reliable sources back to the person who was supposed to be a Native American. If the connection to a Native American is proven using genealogical research in the U.S. Census, Land records, property records, church records and other such sources, then you will see from the Research Wiki page that there references to the Indian Agency handling the tribe when it was transported to Oklahoma. 1862 Census of the Delaware Indians is in the FamilySearch.org Family History Library the microfilm number is FHL Film: 989204. The rest of the information in the Research Wiki article is also very helpful.