Take a look at Beoworld's technical micro-site, and on this page at the bottom you will see the wiring for a 7 pin DIN plug for a Datalink connection between a BeoMaster and its sources e.g. a BeoGram:
http://www.beoworld.org/beotech/misc1.htm
I checked the background of the BeoGram 1700 on Beocentral
http://www.beocentral.com/products/bg1700
and while it was not specific about whether the BG1700 supported Datalink it did say that its successor was the BG1800 and about which it says:
There was no ‘Beosystem 1800’ or ‘Beolab 1800’; this Beogram was designed to work with any Beomaster, old or new. To that end, it was fitted with a 5 pin DIN plug and lacked Datalink, though the electronics existed inside for Datalink use.
So I would say ignore pins 6 and 7 in the diagram which were the data ground and the Datalink pins, and you will have what you want
First B&O (1976) was a Beogram 1500 ... latest (2011) change has been to couple the BL11 with the BL6Ks *sounds superb*