There is no external valve adjustment for the M103 engine in your 300TE. The engine has hydraulic lash adjusters. Are you sure the noise is valve clatter? You might have lost timing chain guide rail or the tensioner. Pull the valve cover and do a rough check of chain stretch.
What's the oil pressure reading through all this noise? How long does it take the oil pressure gauge to peg at 3 after a cold start?
83 300SD ... $950, see cars forum