On my 126, the manuals came in 2 volumes of chassis manuals and a separate manual just for the engine. Couldn't you just get the chassis manuals for your 124, but the engine manual from a C220? Of course a few small things might be a little different, but I bet essentially most things are the same.
'86 420SE Euro
904 Midnight Blue, Gray Velour
Dad bought it new, now I own it.
"A Mercedes-Benz is like a fine wine, it only gets better with age."