Fox,
I am not a blade smith, but I have hafted a few blades. The easiest way is to make the haft as long as needed, drill or punch the holes, then mark and drill the scales for pins or rivets. You can also make a longer tang, and drill a through hole in the handle material and either use a cap screw, or peen the tang over to hold everything tight. Then shape the handle to suit.
Hawkdancer