The above is correct. If you want to really control the timing you will have to go electronic. I have the FAST to control all the timing and imputs for most situations. The 6A that I have supplys the spark when the FAST tells it to. The distributor is locked out so it only distributes the spark to the individual cylinders. Really simple arrangement and it works great. I need to swap the 6A for the AL so I can have the rev limiter.
Go to the MSD site and look at their videos. They have a bunch of them. They explain the 6A, 6AL. And 6AL2. About the only difference in the 6A and AL is the rev limiters. If I remember correctly the AL you install the buttons(limiters) and the AL2 you dial them in. Equipment wise you will have to add the FAST box, a crank trigger to alert the box the next signal it receives is the #1 cyl. The MSD distributor will then do its job in distributing it.
Hope that helps you.
Bill