Blair et al -
I may be out on a limb here but I don't see this blade as suriage. The hamon starts at the machi and the jiri looks correct. Are we sure we aren't looking at a kodachi here?
And if so then the soe-bi appears to have been polished away leaving only what we see on the nakago. That is what I see anyway.
Blair - blade length is one indicator of blade type, placement of the signature, and age may also be determinants. The koshirae if original could also make a katana out of a shorter blade if that is how it was worn. We have to be flexible sometimes with our understanding of these terms. If the age is correct the blade you post would be a kodachi I think and if later a wakizashi barring any other evidence.
Koshizori appears in the lower third of the blade, not just the nakago - the machi are something different altogether neither have much to do with prayers. Perhaps you are thinking of Gohei-gata nakago, a unique shape of tang that looks like the sacred paper of a Shinto shrine.
-t