In my opinion it is very unlikely that 16th, 17th, 18th and 19th century American/British families ever used Elijah for Elias. If I saw the two names, my first thought would be that they are two different people until proven differently. The reason being that although Elijah is Elias in Biblical Greek (Koine), the reference is in connection with the 1st century Christians who had Jewish lineage but were using Koine Greek for the New Testament or possibly the Septuigent (Old Testament Greek translation) written hundred of years before that. For American genealogical purposes, I doubt early Americans knew of the connection, and were most likely taking the name from the New Testament (like in Matthew 11:14, King James Version of 1611 translated 'Elias', but re-translated 'Elijah' for 20th century translations like the New International Version), completely oblivious to any connection with Elijah.