I bought a LX3310 that came with the 72" MMM and after the first mow I knew I wanted spacers. I bought 2" Bro-tek spacers and I took the mower arms to a welder and he cut a wedge out so he could bend the casters out 2".
Spacing when stock
Spacing with 2" spacer and modified arms. Note that this method brought the casters closer to the deck. At this height they don't hit but if I were to lower the deck more the left caster may have trouble spinning. Maybe if the cut was made farther ahead this wouldn't be an issue.
without vs with 2" Bro-tek spacer
One note about the Bro-tek; I would recommend buying the additional four lug nuts and lock washers from them so you have a full set. Their kit re-uses the four stock (two per wheel) flat nuts and lock washers. The stock are 22mm vs the bro-tek lug nuts are 15/16". Also the stock lock washers spread when using the torque specified in the installation instructions.