I got my changeout wheels/tires from Scott at:
www.trailertiresandwheels.com
in Edon, OH. He is very knowledgeable about this type changeout.
Got mine done in '07 and have more than 20000 miles--no problem. Cost was around $1800 at the time.
The wheel/tire combo is almost the exact same diameter and about 1" narrower--4805lbs capacity.
Joe