OMG, don't let these guys discourage you.
I drive with 4.56's on the street. Started in 1982 with a 72 Demon and it had 4.56's.
Still doing it today. Guys like ebooger have been telling guys you can't run lower than a 3.55 for decades.
I can tell you 100% that a 750 with mechanical secondaries won't kill your bottom end and make the car undriveable. You can then use the 750 on the 360.
The earth is not flat and just about ALL the mathematical formula to calculate carb CFM are wrong, have been wrong and will continue to be wrong. This is proven in the real world very day.
Nothing wrong with what you have planned. Headers, cam and carb plus your 4.10 gear sounds pretty normal to me.