I have an MSD Digital 6 on my 82. I am currently using the distributor to trigger the box directly and have removed the Duraspark box. I bought the MSD harness that plugs into the dist plug. I have Taylor Spiro Pro wires.
I originally set it up using the Duraspark box to trigger the MSD, but decided to simplify. Not sure if you can trigger a 6 AL directly from the dist or if you need the Duraspark box. The directions should tell you, otherwise call MSD.
I am using the plain old Duraspark Dist, with the stock mechanical and vacuum advance and it works fine. I currently have the vac disconnected, but it works fine when I want to hook it up for street driving. I would stay with the Ford unit until you want to spend the xtra money for the MSD. That said, I would like to get one with a fully electronic advance setup vice the mechanical and vacuum stuff.
If you use the stock dist, the mechanical and vacuum advance should work just as well as stock, and you do not change them at all.