8-position rear wheels can be had as an option for most all of the 2000, 3000 and 4000 Series of John Deere tractors. Thus, tire/tread width can be adjusted without the need for spacers.
Just make sure you have these types of modifications done as part of the setup before delivery. A local dealership charged $320 to pick up and return a tractor -- John Deere 4005 -- which had the rear wheels moved out to set the tread widths to match front and rear. (John Deere recommends -- along with proper ballasting -- that on all series tractors utilizing the 300, 300X, and 300CX Loaders, the tread widths of both the front and rear tires be the same.)
TMI ....
Joe