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.
i don't thimk they are any more reliable than the stock duraspark set up.i had an msd pro-billet and msd6al in an old 2wd with a 351w, which was built up pretty decent....i didn't notice one bit of performance difference.
but it did clean up the engine compartment up.:doh0715: