I certainly don't envy you having to wrestle that weight onto your tractor's rim. I think you might have the best luck handling it if you make up a hook similar to one that BHD linked to and built it to ensure the top arm clears the top of the fender so it will lift it evenly. Get the tractor as close as possible, jack the wheel up, align the holes to the studs and then work the weight over. Maybe have something like rope blocks or comealong to pull on the cable lifting it just to have better control of it in the in/out direction.
That being said, you would have had a LOT easier time getting it bolted up if you had installed lengths of 3/4 pipes where you installed the bolts.
Hindsight is always 20/20. Oh well. Then you could have temporarily used a long length or two of all thread to get the weight lined up and sucked into the rim where you could have installed the permanent bolts.
Six 5/8" grade 8 bolts are overkill too. For that weight three grade 5 bolts would be way more than adequate.