It is clear that all of the fittings are cast copies. Look at the photo in the museum book - every pore on the dragon's snout is carefully carved. Then look at the Tachi for sale - typical "melted" look with loss of detail due to the casting process. And the other fittings all show casting bubbles, with the carved vines clearly just cast in.
The Horimono work is VERY poor, and looks new, which it must be, as who would have done such poor work in the Samurai era? I have a modern copy of an older blade, made in the 30's, that is 50 times better workmanship than this.
I wouldn't offer $2,000 for the whole rig. Just wait a few years, and you can get a better Tachi from China for $500
