The 'rare bird' Rolex ref. 1630 was introduced a few years earlier than the Oysterquartz as its predecessor —at least from a case and bracelet standpoint. While the stainless steel version of this watch was named Oyster Perpetual Date ref. 1530, the two-tone version bears the name Oyster Perpetual Datejust ref. 1630. 

The ref. 1530 was fitted with an integrated 'Oyster' bracelet while ref. 1630 came with an integrated 'Jubilee' bracelet. A timeless and very 'Gerald Genta' looking design that would later be adopted by the Rolex Oysterquartz. As you can imagine, very few 1530s and 1630s were made in the 1970s.

For this particular timepiece, the reference number marking is located on the back of the case right behind where the 1 and 2 o'clock markers would be located on the dial. The serial number marking is typically located on the opposite side from where the reference number is engraved.
This Rolex ref. 1630 came fitted with an integrated 'Jubilee' bracelet code 96673 in 14K yellow gold and stainless steel. The main difference between the two-tone bracelet in the Oysterquartz ref. 17013 and this one, is that the bracelet on the Oysterquartz comes with two gold center links while the bracelet on the ref. 1630 has three gold center links. It is very common to have unscrupulous sellers replace the bracelet of the ref. 1630 with the one on the ref. 17013 so be very careful.

Another difference —besides the obvious difference in movement and dial imprint that doesn't say Oysterquartz— between ref. 1630 and the Oysterquartz, is the presence of a flange with a minute and half minute track. Something worth mentioning, is that ref. 1530 came with a minute track flange with the same layout as the one one on the second picture. As far as we know, all original flanges on ref. 1630 show the minutes and half minutes, while service replacement flanges only show markers for the minutes.

Without a doubt, the Rolex Oyster Perpetual Datejust ref. 1630 is one of the most iconic watches of all time and a clear example of an era influenced by flat top cases and Royal Oak inspired designs. Long live the Rolex ref. 1630.