Okay .... I'm stupid! Found it! The kanji I couldn't make out is 住 (juu/reside). I found it in another book I saw today at Kinokunia: The Yasukuni Swords: Rare Weapons of Japan, 1933-1945, p. 25. This page shows a sword made recently by a former Yasukuni smith, and his writing of 住 is exactly the same. So, mystery solved!!
I normally recognize 住, but this stylistic form had two extra strokes instead of a single long stroke. Anyway, I was thumbing through the book and there the kanji was, right in front of me!!!
So, your entire tang should say something like this:
"su" Noshu Kitahara Juu Hiromasa Saku
[su] Made by Hiromasa, Resident of Kitahara, Noshu [Mino Province]. Do you notice that the word order is almost entirely opposite that of the English? That makes Japanese "fun!" .... not!