Im not shure. I use it for my 72 in hustler and it does just fine. A tractor type mower may be distributed differently with the motor in the frontI have a MoJack Pro and it is rated for 750 lbs. Don't forget that your back wheels are on the ground and depending of the weight distribution will carry much of the weight.
I personally would not use it to lift 750 lbs but since your tractor weighs a total of 890 lbs, I would be surprised if more than half of that weight is on the front wheels.