I have a shallow mount CVT that was in my single cab Ranger before I sold it. It was only used from March of 2012 to October of 2012..
Dimensions of the box are: 13.5" tall, 21.5" wide, top depth is 3.5", and the bottom depth is 7" It should fit under the rear seats if you did some slight modifications to the bottom of the seat..
If you're (semi)local I can hook it up and let you see/hear that it works perfect.
Looking to get $150..