I'd say that that looks like a good disk. However, I think most people prefer the cast, pillow block type bearings rather than the sealed type. At least that is what you see on the heavy duty disks anyway. Still, what you've got there is exactly what I'm looking for! I think you have a great find.
The height problem is exactly what I was talking about above. I think with 3-4" of clearance you should be fine. Just go slow. If you do catch it on something the disks will roll, just make sure whatever you catch it on isn't too hard (rock, concrete) or too nice (lawn).
Can't wait to hear how it works. I'm very jealous!