I am going to look at it w/ a scope...but I have never seen the insides of an 603. Besides the obvious broken metal what should I look for?

I can find the 6 cylinder 603 but it's hard to find the 2.5.
Will the 3.0 fit w/out major modifications? Did the front spring rate increase when they went to a 3.0 in the 124?

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82 300D....went to MB heaven
90 350 SDL....excercising con rods