I had my chain guides already in when I did mine - I tied some speaker wire to one end of the chain. I fished it through the timing device side of the engine, then slid the other end of the chain down the other side (with the long guide). I was then able to tie the other end of the chain with speaker wire. Then I put the cam and sprocket in, and held the chain somewhat loose while I had a friend turn the crank to the correct spot. I was then able to carefully put the new link in place after setting cam timing to the correct spot, and put it my chain tensioner spring.

This was with the engine on an engine stand. If yours is in the car I don't really see a way to do this job.

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Milan Brown 1979 240D, rebuilt OM617.952 turbo diesel, rebuilt 722.315 transmission - engine spun a rod bearing, sold to pick your part

1979 300SD, ~90k original miles, all stock