A kit for modifying a wheeled apparatus comprises a set of caster unit mounts, a set of caster units, a subframe mounting structure, and a subframe. Each caster unit mount has a caster unit mounting structure and a main frame engaging structure attached to the caster unit mounting structure. The main frame engaging structure is attachable to a main frame and/or a load support structure of the wheeled apparatus. Each caster unit has a mounting portion configured for being secured to the caster unit mounting structure of a respective caster unit mount such that a first-size wheel thereof can rotate about of a rotational axis thereof and pivot about a pivot axis thereof. The subframe mounting structure, which is attachable to the main frame, has a first end portion pivotably attached to the subframe mounting structure and a second end portion having a second size wheel mounting structure integral therewith.