As I recall the present rail on most of SVRy's mainline is 80lb. Someone correct me if I'm wrong. We have some 75lb rail in the McEwen yard area that is from the S.Baker yards that was probably from the rail relaid there in the late 30's which was 2nd hand from UP. There is also a bit of 90' in the yard and I beleive the 2 rails used for the pit track in the shop are 133lb rail donated by UP and are continuous 100' pieces the length of the shop. I understand they were moved from Baker years back using the "Agricultural Approach" for moving over length, over width or or weight loads, that being sneak out of town at first light on a Sunday morning with the axiom "it's easier to ask forgiveness later than to ask permission now". Must have been an interesting show. SVRy has quite a bit of 70lb rail stock piled, but someone told me they couldn't find joint bars on site for it. I never got around to confirming this back when I was more involved. I believe it came from UP's abandoned Jameson Branch and the 80 lb came from the abandoned line between Weston and Athena, Oregon.
In 1938 the old SVRy relaid the mainline with 60, 70 and 75 lb rail leased from UP. Prior to that the main was 45lb.
Today, and Smitty can correct me, because SVRy has virtually no bad ties (ties that will not hold a spike, which is not to say a tie here and there isn't ugly), about the only problem track inspections encounter are the occasional sheared joint bolts usually in the Spring.