I just had the chain, tensioner, and guides changed in my 1977 450slc at about 130k. I use the chief MB mechanic in Corpus Christi because not only is he good but he works on the side for less than half what the dealer charges. He only charged me $180 labor; I bought the parts. I can make $250 a day at work so the economics are really for letting his do it. Plus he did all the front end bushings, ball joints, upper A arms, etc. for $200 labor so I gave him both jobs. Too cheap to turn down.

When he was finished he told me that the chain was good and the upper rails were not that bad. He said that he has seen those 450 engines with 250k+ on them with the same chain. I am an industrial mechanic and work around a lot of chains and sprokets and as a rule never change one w/o changing both. I asked my mechanic about this and he said that unless you can see noticeable wear on the sprokets (there is a gauge to measure this) there is no need to change them.

As far as I know you need to remove the driver's side valve cover in order to access the guides on that side. The chain is fed in through the pass. side and there are guides there too so you need to remove that side also. The rail guide pins don't really get much wear so I doubt that they need replacing. Again, you are there you might as well.

I made my own small slap hammer for removing the guide pins but ended up not using it. I have a small lathe so it wasn't difficult. I think that you could just screw a 6mm (I think that that is the size) bolt into the guide pins and pry it out.

I think that the quality of either chain tensioner is about equal. I can't remember which one I bought but there can't be much difference in either one.

I think getting the chain installation guide would be worth the effort if you are doing this job by yourself. I can't say that I would reccommend doing it by myself since you really need someone to turn the engine over ans someone to feed the chain.

If you change the sprokets (not reccommended with only 100k on the last rebuild) be careful about the timing. You can get a tooth off and bend your valves with no trouble.

I think that I would start out by measuring the play in the system. If you have play but the sproket teeth are not noticeably worn I would look at the guides, tensioner, and the chain. I think all these parts cost me about $150 and if you are going to do one then do them all.

Good luck.