The boom has marks where the bucket was hitting so it was moving all the way. Has to be something holding the bucket or the cyls. Unhook the cyls run in and out, if they do then put down psi on the boom cyls and see if bucket well come up. If all is ok then it has to be the wrong bucket. I know you said it's not hyds how did you come up with it's ok?
That's the way that they were made at that time. Back then you could buy a retrofit kit but it was pretty expensive. If you take the quick attach off and run out the cylinders they'll break because you have the links at the bucket end which pull the cylinder down and bust the cylinder. I did this once and never did it again. You may want to reweld the bucket and add a couple of inches to the bottom of the quick attach plate on the bucket to give you more curl. Good look because it gets complicated.
Thanks for the info, was going to take the quick attach off and retract the cylinders, you probably saved me a lot of problems. Don't fully understand how welding an extension would help. Thanks for your help