Without knowing anymore information than what's already posted and assuming this application is properly set-up with rear-end gear and transmission stall...

28 to 31 squirter with a 30cc pump on the primary (pink cam quite possibly the black version to cut it down by 20%)

31 to 35 squirter with 50cc pump on the secondary (brown cam)

...or three... ditch the Demon for an HP Holley

Again I know nothing about your application but with a 750 carb and a 408SBC that's the range you'll see. Also consider timing curves, fuel pressure, float settings, and engine temps.

There is soo much to tuning but I believe that will get ya in the right direction.

~Ty @TLI/TPC