If the bucket curl can lift the tractor, I don't think you could have blown anything in the lift arm cylinders. If you put the loader in float and then try to lift the front end with the curl circuit, will that lift the loader, or is it "stuck" to the point that you still lift the tractor?
Also, as dex mentioned, hook the lift arm hoses up to the curl circuit and see if the cylinders work correctly. If that works, then you may have something wrong in the valve.
-rus-