360 Carb input
Its a matter of CFM....required for Maximum Air Consumption.
360 c i...... X MAX RPM........ / by 3456 = CFM
360 x 5000 / 3456 = 520.83 CFM
360 x 5500 / 3456 = 572.91 CFM
360 x 6000 / 3456 = 625.00 CFM
360 x 6500 / 3456 = 677.08 CFM
360 x 7000 / 3456 = 729.16 CFM
360 x 7500 / 3456 = 781.25 CFM
These numbers are pretty close to the Air a given Cubic Inch Displacement engine will move......
A 650 cfm carb would probably be best suited to your engine....because the smaller venturi's...the engines' Vacuum Signal to each cylinder would be improved.
I usually like to lean to the performance side and use a 750 on a 360 because it has larger venturi's and hence less air restriction......and a 650 or less on a 318.