Welcome to the forum, but wouldn't the force be very dependent on the max-load plus a bit so it isn't working right at the limit?
Also, unless I missing something from the very sketchy description, this sounds pretty much like a simple Trigonometry exercise.
As to a cam, again unless I am missing something, would that not only work in one direction? How do you bring it back?
Do some research on electrical linear actuators. Might have just what you need, for a price.