The old springs were on there for about 21 years. I imagine they have lost some of their tension over the years. Plus The machine shop was measuring the springs with the inner spring compressing at the same distance as the outer. In reality it sits about .22 shorter than the outer. That would bump the old springs above 500 open pressure. I bet the springs are real close in spring rates. My thoughts right now is the pressures are close to what the were. The cam has lived for 30 years. If coil bind turns out to be not an issue the. I will run them. Maybe I am wrong but the machine shop tester seems to run high. I am installing the 273 rockers as well.