fordman, I also have a 78 Bronc. The third menber type is the easiest to change. You have to pull both axles, driveshaft, unbolt from carrier, and it's out. I would suggest getting a repair manual as reference. If you change to a different ratio, you will have to change front also, so it's double the work. However, now's the time, cause you have to change one anyway. Personally, I drive mine on highway a lot, so my 3:50 keeps the RPM's in line. Just depends on how you use it, I guess. Good luck. Don