Purchased from Kinokuniya in Tokyo who bought it as part of a collection of unusual weaponry. Unfortunately it appears to have been overcleaned by a previous owner but there is still good patina visible. In the hand it feels old and authentic, is gorgeously balanced, fast, smooth and feels great. While I cannot be 100% sure in terms of age (it is very unusual) I would agree with Kinokuniya who told me it was from the Edo period.
Measures 33.8 cm long x 16 mm wide at center by 6 mm wide at tip. One tip is Weighs a hefty 12 ounces (340.2 grams)
$450 plus shipping