haven't worked on your exact engine but on my 420's and 350 a new chain is replaced using a "C" clip on the connecting link.
if you're removing the original chain use a grinder to grind off one of the links. really easy just cover up the open areas of the engine.
1972 350sl Red/Blk 117k
1988 420sel charcoal/Blk 140k
1987 420sel gold/tan 128k
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