I think I've found the one you want. Rory Block and Lee Berg duet on a gospel-sounding 'Long Journey' on Woodstock Mountains 'More Music from Mud Acres'. It has a chorus: 'Oh my darling, my sweet darling/My heart breaks as you take your long journey'. It is credited to an R.Watson [unlikely to be Doc, as his name was Arthel]. Unfortunately, there is no lyric sheet. If no one else can readily supply the lyrics, I will transcribe them for you later.

--Stewie.