Thanks Firepit!
I purchased the wheels form Caster City. The part number is 3ABK3X-ER21-ML;
http://www.castercity.com/eshop/10Expand.asp?ProductCode=3ABK3X-ML&ReturnTo=../cm3a-stem.htm
The leg frame is roughly 2" dia so the 1-13/16 expanding rubber stem was a perfect fit. I can't recall how much I cut off, but if you cut it even with the other side, where the factory wheels are mounted, you should be o.k..
I used a die grinder to make the cut (A hacksaw would work too) and a round file to trim back the burs on the inside. Keep in mind the metal is not very thick, so don't get agressive with it or you can bend the ends in making it difficult to insert the stem. Additionally, I drilled though the legs into the rubber so I could run a screw in to keep it extra secure.
I had bought four wheels to do all four legs, but it was too much of a hassle to get the other side done. It actually worked out well as I believe it is easier to handle than it would have been with four casters.
Hope this helps! Good luck with the mods. I've got my unit exactly where I want as it performs flawlessly!