Peter - I'd guess it's a retrofit if it's an 1982. Somewhere in 1983 380 engines were built with a double row chain.
If the chain has play like is described, I'd change it immediately.
2003 S500 Black/Charcoal
1990 560SEL 61k Arctic White/Grey
1988 420SEL Black/Palomino Sold @ 85k
1987 420SEL Midnight Blue/Grey
1986 420SEL Diamond Blue/Grey
1983 380SEL Champagne/Palomino