if your rear wheels bolted the axle, then you can get a spacer that spaces that wheels out enough for you to run chains. well I hope this image from John Deere parts makes it in the post. It is part # 17.
http://jdpc.deere.com/pimages/MP12/MP12856________UN01JAN94.gif
16 BM22725 KIT AR WHEEL SPACER (ALL-WHEEL STEER ONLY) (SUB FOR BM18021)
17 M117609 SPACER 2
18 19H2109 CAP SCREW 8 7/16" X 1-1/4"
#17 --- BM22725
http://jdpc.deere.com/pimages/MP12/MP12856________UN01JAN94.gif
16 BM22725 KIT AR WHEEL SPACER (ALL-WHEEL STEER ONLY) (SUB FOR BM18021)
17 M117609 SPACER 2
18 19H2109 CAP SCREW 8 7/16" X 1-1/4"
#17 --- BM22725