Drew in Australia here. I am currently putting a 4.5L MB V8 into my 1965 W111 finny.
See drew56cus - Photobucket - Video and Image Hosting
for pics of what I have done so far.
The engine bolts right up. Just need a bit more clearance around the back of the MB auto - I went full on and transplanted a piece of the tunnel to keep the stock floor shift and driveshaft centre bearing, but you could get away with less work.
Use the V8 radiator (without the oil cooler) - just swap the finny radiator sides for the W108 ones, and with a bit of tickling it will go in.
I also used the W108 V8 driveshaft and rear end, to get a better diff ratio and disc brakes on the rear.
As for wiring, I have been told by my advisor who has done one before, that if you have a F.I. finny, the changeover for K Jet is pretty easy - though haven't got the wiring diagram off him yet.
I started off trying to put a Ford 302W into it, as a guy in the club has done it. I found that the sump pan got in the way of the drag link, and the steering box (it would be the idler arm in a LHD car) got in the way of the starter motor. The way around these issues is to sit the motor up high in the engine bay so the pan is above the drag link, and use a gear reduction starter. Castlemaine rod shop in Victoria Australia even make an adapter kit to take care of engine, g'box mounts and speedo cables - check 'em on the web.
There is also a US based web site (can't find address now as computer blew up) all about 302-351 V8's into W108 cars. They have lots of tips on there.
Don't know much about the SBC, but I am sure the 302-351 site would have someone in the know...
I found that the MB V8's are easy to find now as there are lots of old W116 450SE's falling out of favour with the fuel prices.
Now, the main difference from what I have read over the years with the W110 and W111 is the length of the car in front of the firewall. The W110 is shorter. So it may give you more headaches in trying to squeeze the radiator in the std place - though there is plenty of room if you get rid of the mechanical fan and use a thermo...
So the glass and doors etc should be interchangeable, but the front sheetmetal is not.
And the heckflosse group are pretty awesome... lots of knowledge there.
Good luck with your decision!!
Drew in Oz