596 casting or 308 casting for mild 360 4bbl

Get the 308 heads, there is as much "swirl" tech in them as a j head, only diff between the 2 is the better exhaust port and tighter pushrod pinch. Last set i ported went 267 @.500 3/8 stem 2.o2. Throw some 11/32 stem 2.o2 valves in either head and they'll flow close or about the same intake wise, 308 heads will trump the 596 on the exhaust side however.
Ultimately the heavy car with the aforementioned 360 will move well....but if you want tire ripping muscle, stroke it and use either heads and you wont leave potential for disappointment.