hi jim,
sorry for my late entrance. i missed your call on this one. and so, all relevant information has already been said!
i also agree with lew, that the blades were also joined via a peened-over shortened tang, which can be elongated to resemble a dovetail.
the attached image is an old example, of the early 17thC. the blade sits into a cut out slot in the guard (quite shallow as the guard is not thick) and a small tang has been peened over.
you would think this is not a sturdy way to join the blade, given the stabbing purpose of the dagger but it is 400 years old and still solid with no movement.
delor, with these three ways of constructing a katar, i think you have a free reign. if you want historical accuracy, why not roughly design the katar that you have in mind, and show the drawings. we can then tell you what it is close to (ie which culture), and show you pictures of actual examples of the same type. you can then adjust the drawings to suit, and you fit the blade in the appropriate way.