The timing chain in the 61x series engines has no set lifespan, but regardless the lifespan is usually very long. Replacement of timing chain should be determined by visual wear on the chain and sprockets, and stretch as measured by the 2MM method. From having checked and adjusted at least a dozen engines, most of them have been between 3 and 6 degrees - the FSM gives part numbers for woodruff keys up to correct up to 10? degrees.

As diesel911 says, your symptoms will not be fixed by correcting 5* of stretch - you're getting ahead of yourself if you haven't set IP timing and had injectors tested for proper calibration and atomization. Even so, the *one* 617 I've actually replaced the chain in required another 3* compensation via an offset woodruff key to get the cam to 0. Don't replace the timing chain without also at least inspecting the roller bearing on the vacuum pump, and replacing the tensioner rail which involves disassembling the belt drive and crank pulley to get at the pin that holds it in the block.

I math'd it out once and 5 degrees stretch - if it's all in the chain and there's no wear on the sprocket teeth which won't be the case - is basically 3/8" over the entire length of the chain. .0028" per link of the chain. The timing chains on these engines very seldom break on their own - it's usually the vacuum pump bearing or some other related component that takes out the chain. So if you're going to do the chain, there's some other work that should be done to truly reset the lifetime of the system. Otherwise, just leave it together and zero out the cam with an offset key as the FSM says.

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'82 300CD
"Pearl", the very first turbo diesel 123 coupe
Totaled 11/23/18, rebuild in progress.
'85 300TD, "Artemis".
'78 300D euro, "Ol' Red", mostly retired.
'85 300D, "Gandalf".