Quote Originally Posted by Z3_GoCar View Post
Probably the best answer would be it depends. I havn't removed a differential from a Miata, so I can't say no, but on the other hand... Josh's car and mine the differential bushing in the single "Mickey" mouse ear locates the sub-frame so In our case a polly/delrin/or aluminum bushing would be perfectly legal, same as polly/delrin/aluminum would be legal in the sub-frame points just inside of the wheel. So, if it mounts only in the sub-frame or only on the unibody they're not legal, but if it mounts in both the sub-frame and unibody then you might have a leg to stand on.
Interesting argument. I can see the twist that on this car, the differential bushing (where it mounts to the unibody) is essentially a subframe bushing too. But I use stock.