You don't have to gut it; just make some reversible mods under the box. There are two wires attached to the 'E' terminal, unsolder them from the bottom of the terminal. (Depending on the box, you might have to bend the terminal a bit to get the wires off.) Cut the conductor that goes to the 'F' terminal. A Dremel with an abrasive cutoff blade makes really short work of it. If you decide to restore the box, it's easy to solder a jumper over the cut.
Then add a heavy jumper (I used 8 AWG) across the bottom of the A1, A and D terminals (jumping over F). That's it.
When I did my previous TR3A with the 60 amp Ford alternator, I used the original connection between A and A1. Worked fine for quite a few years, but the connection at the base of A1 eventually opened up. That's why I added a jumper this time.