[Jac Mac]

If the car runs cool with bonnet off , but not with it on isnt the problem in airflow under the bonnet, you say you have a large hood scoop, is this sealed to the carbs only so it doesnt creat pressure under the hood & therefore prevent air from coming thru radiator when car is moving. Venting around wheel arches is easy to check, tape some tufts of wool & see if air is coming from that area while moving. Rule of thumb is lots more outlet area from underbonnet than going in & these should be in low pressure areas. Big motor like 460 is a real problem to get air circulation past.