No respnses, so at least I'll move you to the top.
I did do a quick cross-check at an internet supplier to see if your '84 had the same number on the vacuum pump as later models. No luck.
It seems the '86 & later S-class and E-class use the same pump, and it's available. But they show no listing for 85 & earlier S-class pumps.
One would think that it's just a pump, and could be wired and bolted in, and made to work. But, after installing a remote lock system in my '91, I realized the system is a bit more complex. The later model pumps both directions - vacuum and pressure - and is connected to the system with a 6-wire harness. That's about all I can remember about it.

DG