Hello Indiana
I have a few bits of info re Shaws of Delnalyn which you may or may not know about - much of it comes from Victor Gaffney's book, "The Lordship of Strathavon" and/or Bruce Bishop's booklet (ANESFHS) about Parish of Kirkmichael.
Like you I have estimated that William's birth is circa 1754. The first mention of Shaws in Delnalyn (spelling varies considerably) is in 1763 when Donald Shaw married Janet Cameron (a second marriage?). The 1773 rental crop also records Donald Shaw as being [in] Delnalyn. There is a reference made of Donald's son being recruited into the militia which extended the period of his tenancy. 1778 - William Shaw, Findron was recruited into Farquharson's militia. I suspect this is 'your' William and Donald's son. In 1784 William and Donald Shaw were given a 19 year lease of Delnalyn and in March 1785 Donald died. 1790, Willian Shaw rental crop and 1797, William Shaw paid horse tax. If his birth was 1754, he would have been 41 when he married Ephy so maybe he was married previously?
Going backwards in time there is a Donald Shaw, subtenant in Tommachlaggan (1752-54) - could this be William's father? Even further back (1729) is the birth of Donald Shaw to William Shaw Fodderletter and Isobel Robertson - could this be the right Donald? The ages would work as would the tradition of eldest son named after his paternal grandfather.
What I haven't found, however, is how these Shaws are related to my Inchrory Shaws.
James Shaw, son of Donald Shaw, is my 3xgreat grandfather by way of his son Alexander. 'My' Donald Shaw is the youngest son of Alexander Shaw and Elspet Farquharson (Inchrory).
Let me know if this makes any kind of sense to you?!