Finally, finally, I identified this print today. This print has been reproduced or linked to all over the internet with no attribution, so that can finally be rectified at least for Heavenfield. It was produced by Caspar Plautinus, Abbot of Seitenstetten (Austria) in about 1621 for his book, Nova Typis Transacta Navigatio: Nova Orbis India Occidentalis.
This is apparently a book about a Benedictine monk who accompanied Christopher Columbus on his second voyage to America as a papal ambassador and missionary. The good abbot begins his book by recounting the legend of St Brendan. Here is a description of the book from Bryn Mawr Library. The British Library and elsewhere confirm that this print is from that book.