I would guess that they use a batch fire setup where all the injectors fire every time around. That's what I use. Even if you mixed the wiring up and the injector fired at the wrong time, you probably wouldn't know the difference. The amount of fuel injected is so small and the rpms are so high that a batch fire setup is plenty effective on a big block.
Example, 3500 rpm cruising speed, all injectors fire 58 times per second with a batch fired setup.
At 7000 rpm WOT with my setup, the injectors all fire 116 times per second and are open for 6.7 milliseconds. It's amazing that they can respond that quick and run reliably for so many billions of cycles reliably.
When going for lots of HP, a batch fire setup is all thats possible to use because of the fuel quantity that you need to inject. You could'nt get enough fuel in the engine if you used sequential injector timing that only injected fuel every other time around.
Sequential really shines for fuel economy and low end pulling power on small engines and that doesn't apply here.