the 302 small valve heads have the swirl ports, but the 308 large valve have a different chamber design... are you sure they are swirl port? The ones i have are open chamber, and i am not sure if they are swirl or not...
the reason the factory used the huge combustion chamber heads is for 2 primary reasons
---they already had the casting for the 360, which needed the large chamber to pass emissions (mostly nox) emissions, and everyone here knows that if chrysler could use a part somewhere else without redesigning it (to save money and time) they would!
---also, any true v-8 performance in the 80s (from the factory) was near impossible before efi because of the crude emissions systems, any increase in compression and aggressive timing would send emissions too high for a production car. so, the high combustion chamber cc's kept emissions under control. by keeping combustion temps low, nox production stays low
i hope thats the answer you're looking for...