Thank you all for the responses.
Any info on the smith?
Hawley's list a Bungo Muneyuki, but with a different character for Mune. The Nihon-to Koza shinto book merely mentions that there were smiths with that name. Google was no help.
Searching the smith database, I get three hits, the second of which (Muneyuki III [is that sandai?]) has an exact match for this mei, except that the kanji for "Mune" is missing for some reason. That smith was kicking around Shoho, 1644.
As for the blade itself, I seem to buy with the eye and heart. I love this little guy. It's a smallish Wakizashi (nagasa 43.8cm, or approximately 17 1/4") with a deepish sori (15mm), and - to my eye - an elegant sugata.
Edit: here's a (terrible) picture: