SN and RN motor mounts are identical. As stated in the thread above and in the links, the yami couch mounts have the same angle but are a little taller.
Sometimes you can eliminate some of your shims and use them as is with no mods. If you have access to equipment to mill a little of the bottom of the mount, then they mount identical to sj mounts. Otherwise, I enlarge the holes in the mount toward the inside which allows the mount to slide out, thereby lowering its effective height.
The only other problem is their use with kenny keepers, you must clearance either the mount or the keeper to use them together because of their larger size.
Finally, the couch mounts larger size and oem use with larger, heavier motors would indicate higher strength. They have a larger metal plate on top. Therefore, more surface area of metal to spread the sheer load to the rubber before failing.