Mike,
Just off the top of my head quick thoughts:
Higo style rain or water/river dragon . The kozuka being iron is nice. Ones in decent condition seem to be more and more difficult to find, given than the majority of soft metal ones and the nature of iron kozuka to deteriorate if not cared for more than the soft metal ones need. Often the iron ones are Higo or related product.
So I'd hazard a guess yours is probably a Higo product or Edo
I'd guess mid to late Edo. I'm not much into kozuka, so take my thoughts as novice. Hope it helps.
Curran
