The open spring pressure is 310 pounds- but at 0.575" lift. The pressure at close to 0.500 is going to be well under 300 pounds.
I have broken in FT cams w/springs similar to this- but that was then and this is now. I believe if you're careful and follow all the rules
, you'll be OK. But then, I
won't be repairing it if it goes wrong.