Just going by pics, these look very close to what you need. You'll need to press one of the inserts out and measure to be sure though.
http://customwheelaccessories.com/al...l-inserts.html
http://www.prestigewheel.com/Imagewi510.asp
Red Rider's Sand Machine Updated 07/23/14
I was able to use the same ones as a 400ex. Also, the rear wheel hubs to a 400 will fit. I put them on my 250R, they widen the stance an inch on each side.
81 250R Custom
83 250R (in progress)
98 Scrambler 400
03 Bombardier Quest 500
07 Polaris Predator (sold to klondike1020 )
68 VW Dune Buggy
^^^ True statement