By following the hyperlinks above you should be able to recover data about DSG lathes produced from the mid 1930s onwards, The 1960s to 1980s section covers many models - these being supplemented by very detailed entries for the more popular models.
The bulk of the 1960s to 1980s lathe are spread over three pages, this one and page 2 and page 3

Developed from earlier models and of the very best quality and with a prodigious reputation, DSG lathes until the late 1960s were usually assigned a Model designation using a very simple but informative number notation. This method stated just swing (twice the centre height)  e.g. "30-inch" or, one some, included the capacity between centres in inches e.g. "13 x 42". Some were marked with their special application e.g. "30SB" for a model intended for Surfacing and Boring . By the 1970s this had changed to a system that gave the swing over the bed as the first pair of digits and a zero followed by the swing over the cross slide e.g. 1909. Some times the model numbers were rounded up or down, the real dimensions being slightly different. e.g. the 1307 had a swing closer to 14 inches. Again, some were also given a suffix to show their designed application e.g. "1910t" for a toolroom version and "1608ct" for a Cross-feeding Turret type. While many DSG lathes had the model type cast into the bed, others did not - those the identification can usually be found on a plate or included in the serial number..