I had 4 wheeler tires on a BCS 850 until I bought tracks. I made adapter/axle extensions. Basically, two pieces of plate steel welded to a piece of square tubing. One plate had the pattern for the 4 wheeler rims, and the other plate had the pattern for the BCS tractor.
I appreciate all your posts on Tractorbynet in the 2 wheel tractor forums. I saw on your profile you're a chicken farmer in southwest Wisconsin with 360 acres. My wife and I just bought 200 acres in northeast missouri; mostly timber with about 30 acres open pasture. I have dreams of doing a Joel Salatin/Mark Shepard type farm, and any ideas or insights you have would be much appreciated. (I can email you a USDA map if you want). For the immediate future I plan on having a bcs as my only tractor, and get a UTV for running around, hauling brush, etc.