My Slant 6 and the re-do

yeah. The motor came out of a 70 Dart. it will be replacing the slant6 in my 68 Valiant. The Valiant currently has a motor with 3 core plugs in it now. Should I use the tranny that is attached to this motor and just go ahead and pull both the motor and tranny out of the car together when I want to add this one?