I've run the newer version TWM/Borla Stack Injection system since day one. Although it ran pretty good with the included self-learning "EZ-EFI" after a few hundred miles of 'learning', that system is only designed to control fuel. I also had a separate computer programmable ignition box, but I wanted the ECU to do it all, have more scalability, data logging, and so on, so I traded in the EZ-EFI v1.0 for their FAST XFI Sportsman, which accomplished everything I was looking for. The XFI 2.0 is fine, but is overkill for a vintage-looking GT-40, unless you plan to go with a modern fully sequential with coil-over-plug setup, and have full fuel and spark timing capability from cyl to cyl, i.e. 8-1 cyl engines.
There are a few hidden pluses to the Borla system, which I like. The hidden under the manifold vacuum chamber, the under the throttle plate injectors, center mounted fuel rails that properly angle and feed the injectors under the throttle plate, and probably the least noticed but important design is the flex couplings that are unique to the Borla. As these manifolds get hot and you have dissimilar metals expanding at different rates, these couplings flex axially, which help to minimize the interaction between the throttle bodies and butterflies, so they are binding against each other. That can cause rapid throttle bore wear, which eventually results in air leaks when the throttle plates are closed (idle) and all kinds of syncing issues since you have some cyls getting more air than others even when the throttle plates are closed. Getting each throttle body flowing the same amount of air next to each other and bank to bank are one of those key elements to getting these systems to run well. The throttle response is incredible. Not sure what the cfm rating is on the 50mm throttle bodies, but it has to be in the 1000s!
That all said, no one's mentioned the exhaust system and how well it's sealed in and around the O2 sensor(s). This is critical feedback for the ECU, so if it picks up air from an exhaust leak, you are throwing your money away and end up with a $hitty running system. So not only figure out your budget for the stack setup, also add in an EFI purposely-designed for EFI bundle of snakes. People like to blame the EFI for a poor running system, but there's a good chance little or no attention was paid to the exhaust system. Tip: Look for double-slip joints at the header-collector union, V-band clamps at the collector-muffler union, and nice thick header mounting flanges.
I have over 8000 miles on my setup now. Starts cold (tested to 20s F) and I have tested it in stop and go traffic at over 8000 feet, high water (230) and (240) oil temps, 190+ deg intake air temps, too. I've purposely stressed tested it so I could work out any bugs, and in hope that the car wouldn't let me down on a drive. Last thing, if you happen to live in or near the mountains like I do and see anywhere from 5k-11k feet of elevation (810mb ~ 670mb) change during a drive, you can wire in a second MAP sensor so the ECU sees the pressure changes and adjusts the parameters as you drive....nice to have.
In a nutshell, it runs pretty damn good and looks the part to the untrained eye!