Air bubble in coolant system?

[BlueCrew78]

I have a 78 Pontiac Trans Am. It’s got the 400 that recently has been rebuilt. While breaking it in at 1500-2000 rpm for about 20-25 min the hose to the heater core blew out of the block. After repairing, the engine now overheats.. any recommendations? Brand new radiator, water pump and thermostat.

 

[melsg5]

When does it overheat slow speeds or highway speeds?
What temperature thermostat and have you tested it by heating slowly in a pot of water, preferably using a thermometer, to see if it starts to open at the rated temperature?
You said a rebuild, new water pump and did you measure clearance between pump vanes and pump divider?
What is your initial timing and are you using manifold vacuum for the distributor?