According to a book I own titled "Mercedes-Benz Production Models Book 1946-1995" by W. Robert Nitske, the 560SEL and the 560SL both have the M117 engine, same bore & stroke & the same displacement.
The power output, compression ratio and torque vary.
No doubt things may be mounted a bit differently in these two cars, but if they both have an M117 engine, I'd say you could take the info posted by the fellow who provided it and get after it.
Hopefully we'll have some more folks chime in here.
1991 300-SEL - Model 126
M103 - SOHC
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