I can comment on the differences in steering box/steering pump specs as they relate to the various 116 models. The internal valving on the 6.9 steering box unit has been altered to account and compensate for the extra weight of the 6.9 mechanical assembly. In addition, the 6.9 steering pump has maximum pressure of 90 atms, as compared to 82 atms (fairly certain) for the lesser models.
Whatsmore, for the 6.9 range, there are two models of Steering Pumps. One is the more common Sperry Vickers unit, whilst the other is a ZF unit with a larger output shaft seal and probably a larger bearing for that shaft. We have just recently investigated the various changes pertaining to the box and pump and the differences are noted herein. Regards Styria