781s /peanut heads/vic junior aluminum,???w/e head you use,doesnt matter,flow test them to see what power you can make,,,,other wise you are guessing.The number 500 is just a number for bench racing.lots of lower h p cars,,,IE honda,, or other little 4 bangers go faster than BB chevys for a reason.
RPM/gear matching,,weight/hookup,,,are the things you need to consider.
again,my 80 Camaro ran 11.9 with stock LS-5 specs,using z-55 cam,830 holley,vic oval port,hooker street headers,turbo 400, 219/188s. If you want to go faster,improve on that package,better heads would make the biggest difference.