Unless someone replaced your engine with a 3.5 liter one in the past, which is unlikely, your car IS a 350SEL a gray market car that was not originally brought into the US by MBZ. Not the horrible thing that some people may make it out to be, IMO.
Make sure that the canister that measures manifold vacuum for the injection system is also a yellow color-coded one. As far as tune up specs go, I THINK ignition timing is 10 or 12 degrees BTDC dont count that as absolute fact, as I am going on memory here, and that is NOT a good thing
. On my 73 I had to adjust the valves, but I _think_ that your 1975 may have hydraulic lifters again, not sure when they went hydraulic (it may have been 76?). Check the condition of the injection trigger points in the bottom part of the distributor often times oil will get in there and contaminate them. Just clean them up with some electrical contact cleaner. I found that the best spark plugs to use were one heat range lower than the US spec cars.