I have a 1968 c code coupe with a 3 speed. I would like to upgrade to a 4 speed toploader without dropping $2000 on a new unit. I am planning on scouring a few junk yards to pull one. I know there are different versions of this transmission used in different models, which one will fit my mustang? Will transmissions from other models fit, or should I look specifically to get one out of another mustang?