Biggest most massive 4 core rad for a 68 Barracuda?

A thicker radiator core isn't going to pass as much air through it either.
The factory's engineers determined a wider radiator core is more efficient than thicker.
Still holds true today. A new cars radiator may be only 1 inch thick but its surface area is massive. There is very little resistance to air flow through them. The electric fans dont work as hard and little to no grille is required. Just points to ponder