I swapped a MSD 6AL into a 78 Bronco I had a couple of years ago. I noticed a difference in performance, but don't expect a huge horsepower gain with just changing the box. I noticed better throttle response and off idle acceleration. I also liked a rev limiter. If you don't have a tach and want one, then it is a simple one wire hook up into the box.
On my Bronco now I have a full MSD ignition set up,6AL box, dist, coil, (Its actually the same box I had in the 78) and I like it.