I need schooling - old vs. new engines

Along with all the technology features mentioned, the biggest improvement is port flow in the heads. Computer-aided flow modeling has allowed for much better port shapes that allow massive amounts of airflow while still having decent velocity. G3 Hemi 5.7 Eagle heads flow over 310 cfm on the intake side from the factory. I can't think of any factory head from any older pushrod V8s that flow anywhere near that much, aside from maybe the G2 Hemi or Ford Cleveland but those had lackluster port velocity.

Combustion chamber design and valve timing are also huge. Everyone poo-poos the G3 Hemi for not being a "true" hemispherical chamber but those quench pads on the sides make it so much more efficient than a true Hemi at lower RPMs (<3500). The shallower valve angle also improves "tumble" flow (like swirl but along a different axis of rotation) which again increases turbulence inside the cylinder during the intake and compression strokes and thus efficiency. IIRC ideal ignition advance on a typical G3 Hemi is around 22-28* thanks to the efficient chambers and dual spark plugs per cylinder.