Don't forget a bung in the custom exhaust for the O2 sensor.
I think K-Jet systems run on higher fuel pressure than D-Jet systems. You might need the fuel pump/accumulator/filter assembly from a K-Jet car if yours is a D-Jet.
You mght also need the gauge cluster from a later car for the idiot lights. The 350 has a mechanical oil pressure gauge and possibly a mechanical temp gauge as well. The 560 engine will have electrical senders.
Are you sure the swap is cheaper than buying a 560SL?
Are you sure the 350 has a 3-speed? The 3.5l M116 in US trim came with a 4-speed in all applications I'm familiar with. Or is your 350SL the US version that came with an M117?