i'm planning a similar swap in my 63 220Sb. Its definitely getting a manual trans. planning a t-5 from a mustang but i have the four speed also. I'm driving a 83 or so 280se right now with a 4 speed manual, it is a great driving car, but not a big w126 style fan. My suggestion is do the manual if you can. its a little low on power below 3500 rpm but comes on like gang busters after, almost turbo like. And i really hope its a euro spec motor, us motors are way less powerfull. But it loooves to rev. pulls hard to 6000 plus. the manual make the car feel 500 pounds lighter at least. The euro spec 380se i also have driven with more power and an auto feels slower and way heavier.
As far as the swap it should bolt right in with the stock motor mount arms from the early block. the oil pan should fit but if not a 280sl or slc pan will. I could possibly sell one since i have a few m110 engines in parts cars.One thing you may want to look at is hood clearance. That m110 head is enormous. my w111 isnt going to be an issue i dont think but the w108 is definitely lower in the nose. the k-jet is ok but im sure there is power and a lot of mileage to be gained from a tuned mega squirt or haltec efi system. Plus you could turbo charge it
. Ill be watching this. good luck!