RECOMENDED SPARK PLUGS 1986 420SEL

would like to know what spark plug would best suit the 4.2  engine, Bosch super plus part number 7911 V power or Bosch super plus part number 7607 V power ? or are there any other plugs that are recomended, The 1986 420SEL I just bought has not been run in over 4 years. it is now running but very poorly, could this be due to the old gas that was run through it for awhile and could this have fouled out the plugs ? so bad that it does not have enough power to drive on the road or even out of my driveway, Thanks 

OK, so I went with the bosch super plus 7911 but I noticed that when I went to warm the car up before I changed the plugs that the exhaust manifolds on both sides were glowing super red hot after just a few minutes at idle. so evidently bad plugs are not the problem but instead I have a clogged exhaust system. I will cut the pipe tomorrow and see what becomes of it then. 

well I had time to work on the benz today. found that when I removed the exhaust pipe from the manifold the engine ran 100% as it should have, I didnt run it but a few seconds but that was enough to convince me that the problem was not with the engine at all. there is not a MB dealer around here nor a salvage yard that have any of these cars so does anyone know of a good place to get parts from online somewhere? do I really need the cat converter located right after the manifold or could it be possible to move it back some, there is an o2 sensor and the wire looks to be kinda long so that wouldnt be a problem I dont think. any input on this would be helpful.  Thanks

I like BOSCH plugs, and would recommend to fill your tank with a really high octane gas.  I agree that your exhaust is clogged up...probably your CATALYST. 
 
take care,
-mar-

THANKS MASTERBENZ, I will fill it up later next weekend, I didnt have much time to work on it today as some of the parts I need are not avialable around here so I am looking online to see what I can find. so far I have been able to repair most of the little things by using parts from another car I have out back but the exhaust is not on that car or I would use it. I have repaired all of the vac leaks I could find, changed the oil and filter, repaired 2 windows, the sunroof and the climate control system, I have noticed over the weekend that the front end is way out and the front tires seem to lean in at the top causing inner tire wear, something I didnt notice when I bought the car 2 weeks ago. it looks like the tie rods are bent but it was sold to me as a parts car but I am determined to get this one back on the road. I am going to trailer it into town within the next few days to see if our local muffler shop can do some custom exhuast work.  

Don't forget to get the alignment done when you change the tie rods...
 
take care,
-mar-