As an '84, you probably have a dual-row chain. If so, it is pretty simple to pull the right valve cover and observe the chain stretch and wear on the tensioner rail, and bring #1 to TDC and look at the cam marks. At least then you can make an informed decision. If you have only a small amount of stretch, why change?
If by some chance you have the single chain, you need to upgrade to the dual setup - major bucks.
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe