This would be my first guess...I'm betting its off more than you think. Small blocks aren't that issuistic with overheating issues, especially at idle.

 

Retarded timing will cause overheating issues.

Another possibility not mentioned is the thermostat being upside down.

 

Timing, installing the block off plates on the intake gaskets, air lock and many other things could be causing this.

One trick to avoid air lock is to insert two aspirins in the thermostat when installing. The aspirins will allow you to completely fill the coolant in the radiator and dissolve after installation.

Check the timing first, and then check the intake gaskets.

If the car was running cool before this change there is no reason it should run hot after unless something was installed wrong.

This reminds me of the old days for me. The first thing we always wanted to do as a young know it all, was install a larger intake and carb. (I’m not implying your son is one of these only that I was).

My father would always laugh at me and then preach that the best change for instant results is the rear end gear, then exhaust, then intake and carb. Assuming you have enough engine to go with these changes. After these changes he would then suggest that I move forward with other modifications.

You can gain so way more from switching to a 3.70 or lower ratio as opposed to changing the intake and carb. If this change is not enough then start with the other components.

I’m just offering a suggestion from a haunting feeling from my pop!

Willcox Inc.