The British archery magazine "The Glade" ran a series of articles by Mark Stretton on arrowhead forging - one of these was a type 15 swallowtail. I can't remember offhand which issue number covers this but could find out if you like. The issue covers the making of the head in one piece, but I know that Mark finds it easier to forge-weld two pieces together for this type of head.
Cheers, Dave