Chevrolet Repair: Rad overheats, blown head gasket, radiator core

Question
James
I have an old 64 Chevrolet Biscayne with a 230 6 cyl. motor.
The rad overheats after idling for only a few minutes.
I took it in for a flush and fill and pressure check.
The test was good,but the mecanic replaced the hoses.He also said the thermostat was OK.
Still,it overheats.
A friend recomended I use a rad flush solution available at NAPA,and leave it in the rad to do its thing instead of running it through the system as it might harm the engine.
Do you agree?
There is a big hose at the top and the bottom of the rad.Should I disconnect these? How do I keep the solution from running out of the bottom hose? Thanks!

Answer
Replace the thermostat.
Check to see if the coolant is flowing in the radiator.
Usually a car this old needs to have the radiator core replaced.
If it's only a few minutes though, replace the thermostat.
Have you checked it for a possible blown head gasket?