I am on vacation, but I wanted to contribute, as I think the information may be of help. I will supply info of my unit when I return home, Thurs or Fri.. Background is I have a 351 Windsor, with the FAST electronic ignition
and a distributor and coil.
I will try and find the model of mine. My distributor is one with a short cap and is not as tall as standard units because of the TWM FI. You will see with the pics of my unit that there is very little room for these units. As for which style of GT you own it matters most, how far forward you mount the engine. Then things get tight.
As I mentioned, I have both a distributor and computerized ignition. I also have an electronic box, the MSD 6A and a coil.
This box supplys multiple spark for each cylinder. If I had it to do over, I would have chosen the 6AL or the 6AL 2. These units at least supplys a rev limiter(or 2).
https://www.youtube.com/watch?v=k0ig-VRVMuE
The style of distributor that I have, came with springs and weights for timing. This unit also allows one to "lock out" the distributor so that there is no advance at that point. All it does is distribute the sparks. The box, an MSD 6A only supplys the spark that allows the coil to fire. The computer does all the work. It supplys the advance and timing of the spark. This is done by way of the crank trigger
https://www.youtube.com/watch?v=TCHEHPESf60
When you lock out the distributor, you have to make sure that the spark that is sent is correct and going where you want it to go. This is called rotor phasing the distributor as seen in this video.
https://www.youtube.com/watch?v=aWMlNwGW0tM
This eliminates the spark from going to the wrong cylinder(scatter), either before the one desired or the one following it.
I don't remember the diameter of mine being an issue, but the height is with the fuel rails.
Bill