Its because the mount points in the engine bay are not exactly the same in the CRX as they are in the Teg or the CRX SiR. Therefore, in order to get the engine to sit correctly in the bay, you need custom mounts. If you are getting cheap mounts, I suggest Az racing, they have some billet alluminum mounts that look pretty good. Of course, however, I recomend Hasport. They are proven to work well, and they put the engine in the right place (and I've never heard of them breaking as I have with some mounts, ie placeracing).
Pretty much, what I'm trying to say, is avoid welded mounts, they have week points. If you get billet ones, they will be much stronger.