Bang for your buck. 5.9 magnum in a street car or pickup

Putting 360 heads on a 400 engine....will make about the same HP, just at a lower rpm. The 'bigger' heads thing is overdone. If the 360 head ports are oversize for the job, they would work well on a larger engine.
Pontiac used the same heads, same valve & port sizes, on engines from 350 to 455.