Quick magnum question any help?

The head is the head. There are pros and cons to everything but it is not the reason a Magnum engine will get better
Mileage and make more power over an LA.

Assuming ..... the Magnum has F.I. to help with a small tidal wave of issues over a carb. The intake track is dry. The carb has a wet track and has issues in that.
The computer takes over a ton of things at all RPM's, all the time, everyday. Your carb tune is shaky.

Other bennifit's that allow power are thinner rings, roller tappets, and the list goes on.

When there both a carved engine fitted with the same equipment there is no real difference to jump and shout about.