If your axles are 35" apart, then you can upgrade with the kit found at this URL for $119.50:
http://dexteraxle.com/inc/sdetail/1050
If you want to upgrade the equalizer to a shock absorbing EZ Flex, then you you probably want this:
http://www.dexteraxle.com/inc/sdetail/18100
Just one hint. You may be able to get a cheaper price by calling Dexter and asking for the nearest supplier to your location. These suppliers buy in bulk and may offer a lesser price. I called a couple of different ones saving enough to pay for the shipping.