I like those too. There appear to have been a number of versions over the course of their production. Very light due to the dug out back side. I have even seen a very late pair that were drilled. The springs are well concealed too, the Japanese learned this from the French. Notice the tire guides formed into the underside of the brake blocks, lots of good design thinking in them.
These fetch quite a bit when they come up. I have considered a pair for a French bike I have, but alas, my valuation is always exceeded by someone else at auction.