Ron, I agree with your attribution. It seems a Momoyama tsuba, judging by the shape, wave design and goldwash. It is not earlier as seppa-dai is too wide for early Muromachi.
As to attributing it to tachi-shi/tachikanagushi - keep in mind that these are a construct, popularised by Torigoye, and accepted in order to put earlier tsuba into certain categories.
Nothing wrong with that but, there are no sources which would indicate that tachikanagishi (or tachishi) were a group separate form ko-kinko or kagamishi for that matter. I prefer to say early soft metal tsuba.
A nice tsuba, that is for sure.
I have one that is similar in shape, however made of yamagane, you have most likely seen it. Boris Markhasin from whom I have acquired it describes it as a shitogi tsuba utsushi dating to the 15th, beginning 16th century. This might be right, although the shape of a true shitogi tsuba is much different. Here is my tsuba (there are a few pictures there if you care to click "next"):
http://s1150.photobucket.com/albums/o61 ... G_8067.jpg