450slc

Hello, I have recently purchased a beautiful 75 450slc with 150k on it. I am going through the regular new purchase maintenance moves and changing out old hoses and fuel lines. I have noticed the car running a bit rough at idle lately and I suspect it's vacuum related, but I am going to change out the wires and plugs just in case. I have also been considering changing out the timing chain, but I can't determine the difficulty of this procedure and I am not sure I want to DIY it. Any thoughts on that particular job? Is the chain of the interruptive vareity?
Thanks,
S

myway

Here is a tutorial with pics. I can't remember if ii includes the upper guides and tensioner.
http://www.peachparts.com/Wikka/M117TimingChain