I ran the MSD 6A unit in my Cuda for a long time - I bought it in the mid '90s. I kept my Mopar distributor, and kept the ECM and all wiring in place, but disconnected, so that if the MSD box ever went out, I could quickly switch back over to the Mopar ignition and be back on the road. The MSD box never failed, so I have never needed the backup system. I finally replaced the MSD with a Crane Hi-6 multiple spark ignition that has an adjustable rev limiter built in, and put the MSD box in a 5th Ave. I took the MSD box out when I junked the 5th Ave, and if I put it in a car today, it would still work. I haven't had any problems with the Crane box that replaced the MSD box either, so they both have been very reliable for me.

The Multi spark boxes really won't give you more power - they only send multiple sparks at lower RPMs. I believe that by the time you hit 3000 RPM they are only sending a single spark. The thing they do is to give you a better idle, and you might get a little better low end torque due to getting a more complete burn at lower RPMs because of the multiple sparks. However, I've never seen any real world data on that, so you may not get much more, if any, low end torque.

I had the MSD box mounted on the firewall of my Cuda, next to the ECU. When I swapped over to the Crane box, I built a small shelf under my dash, next to the radio, and mounted it there. When I installed the MSD box in my 5th Ave, I mounted it behind the drivers side kick panel. I've also heard of people mounting the boxes under the battery tray. My thoughts on mounting position are that heat causes problems with electronics, so mount it in a place that stays relatively cool, which is why I went under the dash with the Crane box - it may not be the coolest place in the car, but it's cooler than under the hood.

Summit has the MSD 6AL for $205, and then you would need to buy one of their RPM chip kits to set the rev limiter for another $28. The reason I changed boxes in the Cuda was to get a rev limiter (the 6 A that I had has no limiter), and I went with the Crane box because they have a dial adjuster for the rev limiter so you don't need to change chips if you want to adjust the rev limit. It's also digital, rather than the analog MSD 6AL box. Summit sells the Crane Hi-6 for $250.