1.) From light being refracted as it passes through the atmosphere.
2.) That's the point I've been trying to make.
3.) Like I said, turning a $60 afternoon job into a $1600 week+ job. If the rest of the combo is matched to GT40s, then better heads will be held back by the rest. It's seldom a case of just swapping heads. Intake, TB, MAF, injectors.. easily another $1000 on top and now the engine block is a serious liability.
Nick, do you have the blower installed already? How about the GT40 heads? The heads don't have to come off for changing valve springs if they're already installed. Do they have pedestal or stud rockers? The best valve springs are going to be the ones matched to your cam profile, which we also know nothing about.
It would be helpful if you put at least a basic rundown of your car/combo in a forum signature. That way we don't have to interrogate you just to answer a question and you don't have to explain it every time.