I would have to agree... because you have switch more than just trannies... wouldn't have you have to change out engines as well as all the computer/sensor stuff?
I would think you have to do that because all the computer timing and sensors are there for a ATX...I would think these sensors and the pcm would be watching rpms, speed..blah blah blah... I would think it would be more labour intensive doing a tranny convert than say an engine swap.
Just my uneducated guess.....