Do all 67-69 small block Barracuda's run hot? Rant

Owned our convertible for 12 years now, and have tried various combinations of radiators, water pumps, shrouds , fan blades etc. to no avail. Finally determined ( in my head LOL ) that it was an engine problem after finding 18% - 24% leak down in the cylinders.
Built a fresh 340. everything new. Engine ran at a rock steady 180 over the winter months. Now that the heat and humidity is back. it's starting up again. Engine runs 180 for a while, then shoots up to 210. After a while, it then skyrockets. Happens when idling for a long time
Have again verified timing and harmonic balancer, carb jetting etc. Has a brand new 22 inch US radiator's 3 core radiator, larger than the 2 core original. Seems like the engine compartment is so small that the heat gets trapped in when you idle for a long time. Can see the heat waves radiating off the hood after you idle for a while, can't begin to touch the hood. Everything's fine when rolling down the road. Any thoughts?