A manual for a US-spec 84 380SL is about the closest you'll get. I wouldn't bother with a manual for a 450SL because the older car has much simpler engine management and a different ACC system among other differences. You might check the manual for a US-spec 84-85 500SEL for engine particulars but you might end up more confused than informed since there are differences between the European and US-spec M117.

I mention US-spec engines because manuals for US-spec cars are the easiest to obtain.

Sixto
95 S420
87 300SDL
83 300SD