[blykins]

Manufacturing processes and tolerances are a million times better now. Parts are cast in molds that are more efficient....higher pressure....less porosity....or they're forged.

The guys above are right. There is such thing as fatigue stress. I couldn't tell you as much about it today as I could 4 years ago when I graduated engineering school, but in our mechanical design courses, we had to design parts for a certain life cycle. Fatigue stresses along with stress concentrations will slowly beat a part down.

With the price of new parts, I don't see any advantage whatsoever in buying 35-40 year old pieces. I bought a new set of Scat H-beam rods for under $400 with shipping. Forged pieces with ARP rod bolts.

I wouldn't even consider using an old part unless it had been magged, x-rayed, resized, rebushed, fitted with quality fasteners, and shot peened.

By the time you put all that money into that old part, you could have bought brand new stuff.....

Not to say that new parts will never break, but I'd much rather trust a new one than an old one.