Does money or complexity play a role in the decision? One route would seem cheaper and simpler than the other.

The 5.7 is not real expensive and are plentiful. The 6.4s are typically expensive and sometimes hard to find. And the super charged (Hellcat) 6.2 can be even more expensive that the Gen 2 Hemi to buy. Then there's the install costs and that's where the complexity really kicks in. Especially if the original injection and electronics are retained.

Modern engines, like modern wheels and tires on our old muscle cars don't always meet with acceptance.