first of all, great job on the table. Looks like that will definitely give you alot more fabrication space, or clutter space, if you will.....
One thing I found out is I have to add casters in the center on each side. Worried about it sagging over time.
I also would have went with the double locking casters. That would've taken care of the wiggle related to the casters. I spent 5 dollars each on the casters and good ones are about 12. And the better ones have an extra 1/2 inch in height so if I ever have to replace them, they will make the work bench too tall for an outfeed table. Oh well lesson learned.
Don't let that deter you if that's what you want to do. I bet you could find a half-inch of clearance with a router. Might have to add some additional support over the caster, but it could be done.
+1 to Cocheseuga thoughts. If your caster brackets are glued on, You could always flip your table over, shave off 1/2" off your caster bracket with a router, and put the new casters on. To do this, you could just put a couple of 2x4s next to the caster brackets, and make a router sled to do it accurately. If you do this, make sure to take the screws out of your corner supports (caster bracket), so that there is no metal while routing.... If your caster brackets aren't glued on, just take them off, sandwich 2 pieces of 1/2" plywood together, in the and mount the casters to that.
In either case mentioned above, you could add more caster support by putting a triangular brace in above the caster bracket.
IMO, I would change out the casters, because I know all to well, that if I don't do something right, that it will eat at me till I end up fixing it. and now would be the time to do it, while it is still relatively lightweight, without all of the drawers and what not you are planning on adding.