Red,
All the automatics were 4-speed. There was a rare 5-speed manual transmission made by ZF.
Do a search on "shift bushing". You'll find info on the plastic parts that keep the shift lever held tight to the shift linkage. It's a common problem and supposedly easy to fix yourself (I have not done it my self).
Regarding your "clank" at takeoff using the kick-down, I think you will have to have some experienced ears listen to it. Noises are hard to describe with the written word. Perhaps one of our other UK members could meet you and help you out. At least they could recommend a good quality W113 service center in your area. You should not only look at how your exhaust is installed and suspended, but examine the motor mounts and transmission mount. If the "clunk" only happens when you use the kick-down, it could be because the motor is moving on it's mounts! It could also be one of a hundred other things.
Rodd
Powell, Ohio, USA
1966 230SL, Euro, Auto, Leather, both tops
1994 E420