Hello Robert,
a most interesting and unusual dagger. Like pointed out by Ian and yourself could the scabbard be a later replacement but don't think that the handle with the brass fittings are not original to this piece, I have seen a few with brass fittings before. See here:
http://www.vikingsword.com/vb/showth...epublic+dagger
But agree that the horn guard is very unusual. I am already curious to see the restored dagger. And I am green with envy!

Great catch.
Regards,
Detlef