It sounds like you have the correct parts. The tensioner rail is aluminum and has a plastic guide attached to it. The other guides you will be replacing are plastic. Metal guides are used in the older engine, I forget the engine# but its the 450. You do not have to pull the manifold or heads to do this job or timing case removal for lower guides, which I am finishing up now on mine. I pulled my timing case and the lower guides were awful at 85,000 miles/29 years.
You will need a pin puller. Do not use a slide hammer. Make one or buy one. Mercedes source daught calm has them. Replace the oiler clips and clean out the tubes that oil the cams. Get valve cover gaskets and new washers. Might as well get a new tensioner also.
If I were you I would start a new thread. There are guys here like BENZITCH and many others who can help better than myself. I hope it goes well for you and way to go for getting in there and giving it a shot.