It's nice to see that these quality Japanese frames are getting the respect they deserve after all these years. I can remember at the time that some folks would turn up their noses a bit because they weren't Italian with Columbus or Reynolds tubing. My Japanese bikes have given me years of great service, and they still ride great.
I thought the Nishikis might have been Tange No. 5. I just went out to check, but I can't tell because there is a clamp for the pump right over the label. :-)
I would buy this bike if I were you, especially if you know that it's in good shape.
I just used the standard Dia-compe sidepulls that came with the bike. I don't think they would be a problem, as long as you kept them properly adjusted. OTOH, those center-pulls and tektros sure are pretty.
You might need to get some wheels with wider rims. The rims that came standard with ours would only mount tires as wide as 1 1/8" which really isn't wide enough for load carrying.
One last note about the point about frame clearance: The problem with the wider tires wasn't with brake clearance. It was with the clearance between the wheel and the bottom bracket. You might not have the same problem, depending on the frame size. Ours is a 21"
I hope this helps. I'm going to watch this thread to see if you end up getting it.