"I had two 75 pound wheel weights on the each wheel and it was still quite easy. "
I've a smaller tire/wheel combo on my 670. However, concur with Spencer's post. It's not too hard...even loaded. Don't let it get away from you...and keep the kids away, just in case!!! If it does get away from you...don't try to grab it. You're not going to hurt that tire or wheel.
Must make sure ya prop it up or have some help when you lift it to re-install.
I also jacked mine at the draw bar bracket (not on the bar). Please but a jackstand under the axle when you pull the wheel off.
Now, I did have help...but I'm a gimp (from a stroke). After breaking the bolts loose, I jacked mine just enough to be able to spin the tire by hand. After that, I removed the bolts. The last one was a bit of a pain. I left the tractor with the jack positioned as described above and the jackstand under the axle (I was only removing the right side wheel).
To re-install, my helper did lower the tractor a bit (maybe an inch) and then slowly raise it to align the wheel bolt holes to the tractor bolt holes.