Yes, but you are looking at replacing the whole seat. The car is already pre-wired for it, but the seat is completely different. I'm not too sure if the bottom is the same. It might be, but the back is different because the headrest comes out of the seat.
I've changed a window regulator once on a S420 and I've seen the pre-wired plug for the seat adjustment.
Unless you can find a wrecked 140 with seat adjustment and same interior color this really isn't worth the money.