The Benjamin McCashland you seem to be referencing may be the same Benjamin McCashland that I descend from. I descend from Mary McCashland Grant, the eldest daughter of Benjamin McCashland and his wife Abigail "Martha" Lake. My Benjamin McCashland was the eldest son of Oliver McCashland and his wife Abigail Butler. The earliest mention of my Benjamin McCashland was in a 1781 Berkeley County WV will of his great aunt, Sarah McCartney. In this will, he and his sister Mary McCashland (who later married John Lake, the son of Vincent Lake) were specifically named as the children of her nephew Oliver McCashland. Brother and sister McCashland married brother and sister Lake, the children of Vincent Lake and Ann Harrison of Culpeper County, Virginia.
The earliest reference I have been able to find on Oliver McCashland is in Uwchlan Quaker Meeting Minutes of Chester County Pennsylvania in 1772, where he is denied his application for membership. It seems that he had offered to join Abigail Butler's Quaker Church in order to marry her, even though he was a Scotch Irish Presbyterian. By 1775, Abigail Butler McCashland had been excommunicated from the Uwchlan Quaker Church for marrying Oliver McCashland in a civil ceremony. (I assume it would have been in Pennsylvania, although I have not been able to find the actual county marriage record.)
There is a land transfer deed from Culpeper County, VA dated 1827. It is unclear from the body of this deed whether the Abigail McCashland referenced is the widow of Oliver McCashland (who owned this land jointly with Benjamin McCashland) or his wife. However, an addendum to the deed dated 6 Sept 1827 names Benjamin McCashland's wife--Abigail. Benjamin's eldest daughter Mary and her husband Evan Grant were witnesses to the transaction along with Benjamin's sister Mary and her husband John Lake.
Interesting to note that the land was originally transferred to Oliver and his son Benjamin McCashland from Elisha Butler, the brother of Abigail Butler McCashland in 1803.
Oliver McCashland appears in various Virginia County Tax Rolls from 1783 through 1789 in Loudoun County. From 1790 through 1800 he appears on Fauquier County Tax Rolls. Later he appears in the 1810 and 1820 Frederick County Censuses.
I have many records scanned and linked into my public family tree. You are welcome to copy any of my information if it helps you. If you come across anything that sheds new light, please feel free to contact me.