One thing that could have happened, the car was a prototype as you said and went "pop" during development. Thus the reason for the rebuild. If he did it as a safeguard he must have been looking for big numbers. So why use the stock injectors? You said they are stock, I can't tell from looking at the pic but take your word for it, you would know. Could you use the stock injectors and a Boost a Pump? I think the injectors would max out before they would flow that much wouldn't they? They would just go static...
If it is 730hp at the crank est, then it is what, about 640 rwhp? It can't be 730 at the wheels.
That setup looks crude, like an experiment.
One thing is for sure, he spent too much money on it and now wants to get it back. Not going to happen.