Like i said, I'm not sure if you'll find the correct height but i think that's the only way you'll be able to get a rubber wheel. I know you can get the "expander" parts separately and they are designed usually for a 3/8" threaded stud but i don't know if a 2" caster would have a long stud on it. By long, i mean 2-3 inches, enough to put the rubber sleeve that smashes down to expand, plastic bushings, and a nut. I became familiar with this when i put them on my ssp, however, mine are taller because i used pneumatic tires instead of the original weber ones.
That's awesome. I love your pneumatic wheels and casters. Looks very heavy duty. That's a huge upgrade from stock.
These hd/lowes/Amazon casters I think are a hard rubber and an upgrade from stock, although not as heavy duty as your style.