Well, I found a way to get some clarity to those vacuum diagrams… and I hope you are right about the engine being a 716.95 for that diagram is certainly less complicated with there being only 3 vacuum lines off the “Switchover Valve” –vs- the 5 lines coming off in the other 617.91 engine diagram. I think Brian is probably correct about the Switchover Valve on your car NOT being designed to directly effect the tranny shifting unless it was the source of leak(s)… but my one lingering concern comes from my NOT understanding what the function of the middle vacuum line is… this is the one that is shown just below the #71 in the 617.95 diagram… and it goes down, over to, and eventually connects via a 3-way connector to the vent line of the VCV on the injection pump. This arrangement with this connecting as it does to the VCV vent line is a marked departure from my two 123 chassis vehicles from only 1 year prior. The only thing I see that the Switchover valve could be doing with this line is for some reason porting vacuum to the vent side of the VCV under certain throttle positions… and this [I’m speculating here now] would slow down the bleeding effect of the VCV. So IF I’m correct, this would directly effect the way the tranny shifts when the throttle was in a certain position or a range of positions.

But I cannot be sure of the above. I have an 1985 300SD back at home that I might be able to further resolve what this vacuum line & connection are intended to do… but that will have to wait until I return to California!
Sorry I cannot help further now. If you are looking to optimize your car's shifting, eventually you will need to "dynamically" monitor the vacuum being sent to the tranny's vacuum modulator.

Do you have a vacuum test pump & gauge? This might seem complicated, but thank God you don't have a 1985 CA 300SD with the mirrad of "stuff" on this same system... see: http://peterschmid.com/vacuum/1977_1985/617_95/1985_cal.jpg

Best regards,

Sam