I need 1991 300SL firing order & more...
 

I'm assembling an M104 and need the firing order & distributor diagram. I would also appreciate any info on assembling and adjusting the serp belt tensioner pushrod.

The firing order is 1-5-3-6-2-4. No doubt you're aware the terminals on the distributor cap are marked by cylinder.

Try a Search for information on the belt tensioner. You will find more than you ever wanted to know about disassembly/reassembly/adjustment of the belt tensioner.