I don't think the looseness of the big draft spring is going to be your problem with it not lifting. The draft linkage can't go back any further than the anchor plate under that spring no matter how loose it is.
I would look at the spring that connects between the front of the ram cylinder and the center (Knee) section of the control arms. If that spring is weak it will not allow the control valve to be pushed forward with any pressure.
First thing I would do is to reach in and push those control legs forward with the PTO running making sure the control valve goes all the way forward.
One other thing I've run into a couple of times is the intake port in the control valve bushing being blocked by some foreign material. It that little hole is blocked it never will lift till it is cleared.
Did you remove the control valve bushing from the housing?
When the control valve spool is moved forward it opens the intake port and when it is moved backwards it opens the exhaust port. Intake port is toward the back of the bushing and the exhaust is toward the front of the bushing.
I have encountered times when the lift would not go down and found that the exhaust port was blocked with some sort of plastic like from an oil container.
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