Whiteline sent us the first prototype for this brand new KDT928 part, which is similar to other bushing "void inserts" they make for other cars. They were waiting for our feedback before they went to production - we gave them a big "yes, please!". This is an elastomer bushing insert that just pops into place and fills the air gap in the factory rubber bushing. We don't have official pricing yet but I was told the price "should be about the same as similar inserts we make", (so about $35). I have an open order for more, because this thing just flat-out works. Super easy to install (no tools, no effort!) and it firms up the transmission mounting nicely. Now installing this will add a little extra NVH (noise-vibration-harshness), just in case you are wondering.
Amy picked up the Mustang after we installed the insert and immediately came back after leaving the parking lot and said "Hey, something is different here...?" It isn't bad at all, just a little more NVH, and nothing like going to a full poly trans mount bushing would be. It just removes some of the air gap and firms the mount up a good bit. We should have these in stock before too long and I will post up in this thread when they are ready