+1 on the great restro work, it really looks fine. No clue about a builder but 6 straight ridges in the steerer usually means Ishiwata, I believe, at least for that part of the tubeset. Tange also made steerers with 6 ridges, but not sure if any of them were straight or if all were spiraled (like Columbus' 5 ridges), but Tange stamped nearly every steerer they made, AFAIK.