Jeff, I expect that your wires are Beru since they have the metal sleeve around the rubber boot. As far as I know the Bosch wires lack the metal sleeve. The original wires on our 1991 300CE had a small red ID tag (1 thru 6) on each wire to identify which plug it went to. Note that there are similar markings (1 thru 6) on the distributor cap and the valve cover ... making it as foolproof as possible. The Beru replacement wires lack the small ID tags so you have to match the lengths of the new wires with the old ones.

As for spark plugs the Owner's manual specs Bosch H9DC0, Beru 14K-9DU0 and Champion S12YCC ... all should be copper plugs. Recently when I tried to buy Bosch F9DC0 plugs for our 1991 300CE both the local MB dealer and an online website called out a Bosch F8DC4 instead. The dealer explained that the Bosch F8DC4 performs better in that vintage engine. Note that the F8DC4 has a square seat and a gasket while the H9DC0 has a tapered seat without a gasket. If a torque wrench is not available, hand tighten the plug until it is seated in the cylinder head. Spark plugs with gaskets should be tightened an additional 90°. Spark plugs with tapered seats should be tightened an additional 15°.

__________________
Fred Hoelzle