The risers must be high enough that your crosschains will slide easily through the slots with the tire resting on the block. X-link crosschain will require more space yet.. Spacing of the risers will be determined by your crosschain spacing.
Mine are pine 2X6's with particle board risers, a woodworking guy worth his salt should be able to lay his hands on lignum vitea for the boards and Bojonegoro teak for the risers (perfect for chaining up sailboat trailers).
The trick for E-Z chaining is to find the best position to lay the chains on the blocks that will allow you the easiest location of connecting the ends with the wheel sitting on the block.. I prefer the back end of the tractor for the connection as I can reach in and grab the hook end of the side chain easier. (I also made a long hook from a pail bail handle that I can reach in, hook the inside chain end, then work it over the tire along with the outside chain.) Your tractor my have more working room in front of the tire.
If you can't remove the tire and you don't have a jack, this thing is the easiest way I've found to mount chains without driving onto them on the ground and then fussing with the slack. Because the chain can move side to side under the tire, slack adjusting is easy. My 24/12/12 tractor chains are "custom cut" with no extra links inside and only one on the outside. I don't' ever need "spreaders", "tensioners", or springy thingys to take up the slack.
Edited by HydroHarold, November 16, 2012 - 06:36 PM.