A member that used to frequent this forum (Gael) installed a 450SL 5.0 engine in his early W111. He had to beat up the frame rails for the exhaust to fit. You could use more finesse and cut/weld the frame rails or build custom exhaust manifolds.

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Tony H
W111 280SE 3.5 Coupe
Manual transmission

Past cars:
Porsche 914 2.0
'64 Jaguar XKE Roadster
'57 Oval Window VW
'71 Toyota Hilux Pickup Truck-Dad bought new
'73 Toyota Celica GT