I measured two that I have and the core dimensions were 19.25" and 19.75" by 4.7". Overall lengths are 22.5" and 23". I think mine are off early model RX7s (79-81) and they definitely have a different mount for the rubber insulators than the one you showed. Not sure if the later models were smaller than the earlier ones I have, or if you have something else entirely. One of mine has epoxy repair to the core, but at least the bungs are okay (I think)- the other has a split bung. If you get desperate, you're welcome to try my spare.