Brazed on cable stops for only the the rear derailleur and rear brake cable is typically indicative of entry level. However, the stamped dropouts are not the typical 2D stamped dropouts but 3D style. This is still entry level but moves the time frame up from boom era, to at least the very late 1970s and possibly 1980s, though still entry level.

The lug set is Eisho Seisakusho's Racer series and the crankset is a Sugino Mighty Tour, though it may not be original. I doubt the forks are original.

Recently, we saw another unidentified frameset that was very similar to this. Same lug set and braze-ons but different dropouts and chrome on the rear stays. Same serial number location but an NW prefix and a much shorter number string. Generally, when there is a double letter prefix, the first corresponds to the manufacturer. The only Asian maenufacturer I'm aware of with a 'D' are Deki and Dodsun. I have no known serial number examples of the former and it's definitely not Dodsun's format. If it is the same manufacturer as the similar frame and the manufacturer is rotating both numbers, that points towards Maruishi or Tsunoda but both typically stamped on the bottom bracket shell and didn't use that long a number string.

My overall impression is an Asian manufactured, entry level frame, from the very late 1970s to very early 1980s. Did you ever determine what diameter seat post is required?