4sp

I'm looking around W140 S280/S320 on the market, I'm covering up to 500 miles a week and this model would fit the bill. I've noticed that the S280 has a 4sp auto, was the 5sp auto an option? My SL320 has a 5sp which has been excellent, but I'm not so sure an S280 4sp is a good combination?

After much thought I decided to go ahead with the transmission swap. I had a donor car, whcih Ive taken the engine out of for the turbo conversion. Having stripped the car apart, here is what I now know about the system. The 5sp box uses electronics only for 4->5->4. But the wiring...

Im just about to buy a car with a 5sp auto to swap the gearbox and diff over. Nav just had a word with george, and apparently there is an electrical plug on the 5sp box, which mine wouldnt have. Does anyone have any more info on what additional wiring would have to be done? Or if its even...