a neat way Ive done casters for (unrelated) a movable frame to support tablesawas along with the entire backtable, they can be several feet long. making them a bit hard ot move without disassembly.
I put three levelling pads to adjust the frame so its level upon any surface I put a big knob, to turn each of the three levelling pads, that could be a big nut instead. the weight of a car would be too much for just a knob at the end of the spindle.

when the leveling pads are raised clear of the floor it then sits upon 3 wheels, so it can be moved about.. could be 4 casters.
I liked the design because it worked well, then it can be leveled , even upon a slanted surface and was very easy to move when not being used. i dont know if part of that design might be helpfiul perhaps it would help to be able to level it to align bolt holes, when coupling it with the wheels.

the opposite way is to put casters on spindles, and lower them, thus lifting the whole assemble clear of the ground to then move it about on the casters.

I guess the point is you can approach it a couple of different ways.

what you have there looks beautiful.