i have always thought 3.5 belts were due around 100k. are they "interference" motors ? and while you are in there, might just as well do all the tensioners and the water pump. i did that on my wife's 94 concorde and it wasn't a bad job at all. i can't say about the magnum as i don't know how much the engine has changed over the years or how much clearance you have. this is just my experience.