This company makes the adapters for Ford style fuel fittings: http://www.performanceplumbing.com/Pure_Choice.html
I can't find a pic, but this is where I got my Ford style/ AN adapter.

 

With twin T-3's I'd think you want to upgrade everthing, rails and all - you should be capable of making 450-500 HP+ easy and will need lots of fuel to keep detonation under control. You should consider replacing the fuel rails and upgrading line sizes.

I am using this setup: http://www.cartech.net/fuelsystems.htm look at the Renegade system. This replaces everything from the fuel pump (big Aeromotive external setup with tank pickup adapters) to the injectors (big billet rails), connected with 1/2" feed and 3/8" return lines, with Earl's -10 and -8 Ultra braided hose and AN fittings connecting everything.

FWIW, Cartech makes some awesome Mustang and 5.0 turbo systems and accessories, worth looking into.

 

You'll need to upgrade the stock fuel rails. They will end being your #1 restriction in the system. If you upgrade everything but them, you'll still have essentially the same amount of fuel flow to the injectors. And you'll need to upgrade the injectors. Something around 36-40 pounds should be about right.

You probably don't need a fuel manifold. The bigger rails will cover that. EFI racers often use a surge tank in the engine compartment. That set up makes sure you never run dry with a sudden high volume fuel requirement - like drag racing. I've seen a system designed with a 3-4 qt surge tank in the engine compartmanet, fed by a high volume mechanical fuel pump. Then a high pressure fuel pump feeds that fuel to the injection system.

What computer will you be running?

 

This might get expensive. I have a 1988 speed density setup with 19 lb injectors. I was just going to put in a big in-tank fuel pump, big lines then install an boost referenced FMU and possibly an enrichment injector driver for extra fuel under boost. The motor is dead stock right now.

If I went for the full Renegade setup, mass air conversion, new injectors and a larger mass air meter I am looking at $2000 add that to the $2000 I am putting into the turbos and installation (using used turbos), that is $4000 on a dead stock motor! I guess there is no cheap way to upgrade horsepower.