Cooling capacity

I have a 1967 barracuda, plain Jane ‘78 318, 904 non-AC. New radiator, water pump, hoses and 160 thermostat. Engine is a professional rebuild. Starts and runs great, but the coolant started to puke out and looked like the Red Sea. Started overheating during a parade.

So, I flushed the system and got the rust out. Replaced the thermostat. Manual says 17qts of coolant…

I put 8 qts of 50/50 in (and the heater is on Max). The level in the radiator is well above the fins, to the point it’s going to puke. I ran the engine - even drove it a mile. I can see the water flowing in the tank. Rad is still too full and that is with just 8 qts added. It’s currently cooling right now so I can check again later.

Has anyone else experienced this? Does the block retain
8-9 qts?