I am no AMG expert. But I would say that it is possible that such a car was built by them. Back in the 80's you first bought a car from MB, then had it sent to AMG for mods. This cost lots of money so unlike today only people with real $$$$$$ could afford these.
Since it was a custom car more or less AMG would probably do whatever the client wanted for a price of course.
Lots of these heavly modded W126's went to Japan and are recently surfacing. Some were $150k+ cars back when they were bought in the late 80's!
So while I have never run across or heard of a super charged AMG SEC, certianly their could be a handfull of example's out there.
I have run across only the cars with the 6L V8, I think that engine came in a couple different configurations.