Blitz...I don't quite understand your frustration. I understand how the engineering blunders of GM can hamper someone's take on a car, or how dealerships can knock one's spirits, but the 700hp thing is puzzling.
To make monster power, and 700hp in my book is monster, from a car with 400hp stock is a grand undertaking. Bumping a motor's output 75% is no small task. Asking it to be done reliably makes that sereral times the cost. Spending what you've spent and not reaching your goals must be, needless to say, a let-down. I known many people who've undergone massive projects and shortly rid themselves of their creations...once you've done just about all there is to do, you must move on to keep that creativity going. If you keep at it, and there's bound to be obstacles to overcome, you'll reach your goal. I don't know if 700hp is within the Maggie's abilities, you know that better than most...but there are other ways. You've done a great job being a pioneer for the Uber-V crew, of which I am not a member, and I'm sure your efforts have been appreciated. Don't let an obstacle stop you, think around it...you know what I'm saying.
And for the Diablo...let it go. If you think there are issues modding an LSx, sir...you may as well sign up for therapy now, as there will be untold mental/economical/spiritual punishment for cracking-open a Lambo motor. And keep it quiet, should those Italians catch a whisper that someone is molesting one of their motors, well....have a hidden passport and some offshore funds when they pay you a visit.
When Lambo's most recent designer, after being recently hired, visited the Lambo factory, the head of the engine team asked him if he was the one who was designing the engine cover? Said designer said no, he was the bodywork designer....Engine man said"Yeah, what I say....the engine cover".
Good luck and revel in the fact that you are quite fortunate to have such a decision. Be good.