If searches of electronic indexes aren't bringing you success, would a manual search of the records be practical? If you have a good idea where your rural ancestor is living in 1870, searching one or two townships page by page might not take very long and might be the way to find him.
Are you searching a birth index online, when you already know the year and the records are grouped by year? It might be easier to search certificate by certificate, particularly if the records are online or have been microfilmed.
Online finding aids are great, but there are still times when a manual search is the way to go .