Mercedes Benz repair: 1975 Mercedes 280SL, spark plug wires, firing order

Question
Hi there,
I just recently purchased a 1975 280 SL Grey market hard top/convertable. It is running very rough, it says it has 355,000 Kilometers.
The guy I bought it from replaced the spark plug wires, but when I pull 1,3,and 5 the rough idle does not change. If I pull 2,4, or 6 it is considerably rougher only running on two cylinders. There is spark coming from all wires.When I try putting each wire on differnt one 1,3 or 5 nothing changes. Can you tell me front to back, 1 being front, what is the actual firing order?  Or can you give me some ideas what else you think it could be?
Thanks in advance,

Terri

Answer
Answer:
This engine needs a compression test.
At that high of miles, I would suspect the rings are gone.

Mercedes v8 firing order animated
http://www.mercedesshop.com/shopforum/showthread.php?t=152127

Finding parts for Grey market cars is rough.