Not sure what yr your working on. I've got a 65 dart that I installed a 46rh into and like has been said to get the trans up and out of the way you will need to modify the floor pan as well as the cross member. Take your time and its not that hard. There's also different options for controlling od and tc lockup
not to jack the thread but I have a 65 I'm getting ready to do this too. The 46 is equivalent to the 518 correct? And do you simply have 1 switch that controls both LU and OD?