Here's what I could find out. The 116.963 was in the 380SE, 380SEL and 380SEC. The 116.962 was in the 83-85 380SL and the 116.960 was in the 81-82 380SL. I couldn't find a reference to the 116.961. I am not sure if all European models are numbered the same as these, if your car was originally delivered to North America I am pretty sure you have the 116.963. Based on the numbers I am assuming the 116.960 was for the 380SL with single rail timing chain, and the 116.962 was with the double rail. It is possible the 116.963 was for the 380 Sedan with double row timing chain and the 116.961 (which I couldn't find a refence for, but which you mentioned you thought you had) could have been for the 380 Sedans with a single row timing chain.
As for which idle speed actuator you need, I couldn't find any info on that. The partsshop here lists all three as unavailable or out of stock.
1995 E420 - retired
1986 420SEL - retired