Another grail watch turned up the auctions a few weeks ago. This is the famous square Goldfeather. One of the very few Seikos with a square case and one of the few Goldfeathers without the Goldfeather text on the dial. A boring design where the slightly curved case and the high square crystal does not do full credit to the thin GF caliber.
AFAIK, there are two GF models without GF dial text, one square and a "modern" design round cased. Both of these have the excellent feather caseback. All of the square GFs I have seen have been December 1964 production so they must have done a small run at the end of the life of the GF caliber. This is also one of the few GFs with an identifiable designation, the "605010" on the back signifies the 60 caliber and the 5010 case style. This six-digit structure is also quite unusual for Seiko.
If the first one represents the "feather" part, this 18K solid gold cased GF would be the "gold" side of things. The GF is probably the most common Seiko 18K watch as it seems to have been popular for anniversaries and similar.
I was going to do a Goldfeather write-up, but with the holidays coming up, it is easier to refer to this one which has input from one of the GF experts on this forum;http://thewatchspotblog.com/?p=62.