I went from a 4:08 to a 3:97 in my 66' 230SL auto. I liked the 4:08 a little better, a little peppier off the line. Not a big difference, but noticible at slow speeds. At high speeds it revs a little less higher, not much. The big difference was disc brakes, not worth switching axles for alone, but a real nice upgrade. I switched because I had sudden differential failure. I had the axle from a 67' 250SL, so I used it. During the switch I bought a complete 230SL drum brake axle, but decided to go with the disc brakes, it was worth it.
It is pretty hard to outhink the people that built these cars unless it is something modern that wasn't available back then, like electronic ignition. I'm with the Dr., you would have a real dog with a 3:27 in a 230SL Automatic. You need two things to go that high in gearing, more torque and more horspower. You aren't going to get any more of each out of a the W127 2.3 litre motor in it's standard configuration, these engines are pretty good even by today's standards. The SL is one heavy car for it's power, someone on here refered to them as the torqueless wonder. And your peak horsepower and torque come on at around 5500 RPM, not midrange like a lot of regular V8's.
You get used to the sound and feel of these engines as you drive them more and more. But, as the good Doctor has said before, only rev a good running, warmed up motor real high, not a worn out death rattle engine.
