I see your point but your definition of harder differs from mine ordering different pistons and cam to me ain't harder.
And a 512 still needs heads cam carb etc.. That supports 500 hp, it ain't gonna pull 500 hp from stock 440 RV parts.
To me harder is going above and beyond with parts, machining, assembly and spending ridiculously more $$$.
Like if you needed a tunnel ram W# engine that needed months of research and development to make 500 hp would be harder, ordering different off the shelf parts that are probably relatively close since were talking a relatively narrow amount of air flow needed to make 500 hp be it a 2l or a 10l engine.