I thought I wanted a couple of tools on a base with 4 swivel casters as well. I have others on the Shop Fox bases with 2 swivel and 2 fixed. Grizzly sells extra swivel casters that fit those bases just fine, but I found out that the way the base is constructed and the way the caster mounts, there is not room enough for the swivel casters to swivel in the spots where the fixed casters are supposed to go. (Hope that made sense!). So now I find it even more of a challenge to move those tools on the bases I added 4 swivel casters to, only because two wont fully swivel.
I guess bottom line, skip the Shop Fox ones if you want 4 swivel casters, or at least be ready to modify them in some way.
Maybe you could modify the Saw Stop ICS base in some manner, or add a platform to the bottom. That thing has 4 swivel casters and a super smooth up/down movement, and easily moves around the heavy saw when raised. It is about $300 though---