An impeller swap can increase a centrifugal chargers efficiency, thus allowing for a higher volume of air per revolution, which in turn would increase manifold pressure without swapping out the pulley. If that it actually the case in this instance, I can't say.
Plenty of cars running blowers with compression out there. Pull some timing out of the top end of the tune and keep the tank full of 93-octane and he shouldn't have a problem.
Doubt he'll want to pulley it for 13psi though. I'd keep it in the 8-9psi range.
IMO, a Novi 2000 is wasted on that engine. He'll never spin the power to it's full potential with that compression ratio. Not saying it won't work, but he'd do just as well with something a little smaller IMO.
Yes. Nitrous and compression go hand in hand.
Sounds like you have a lot to think about. I'd sit this one out and decide what you really want to do with your car.