Overheating

67 Pontiac Bonneville
V8 6.6 liter 400cib
58000 miles

I can't figure out why its overheating. There is no white smoke from the exhaust. After a few minutes of driving the temp boils to 240 degrees immediately. Once I'm stopped I remove the radiator cap and coolant is spraying like a volcano. I thought that white smoke meant a blown head gasket or cracked heads. My driving the care is like Ms. Daisy; I don't peel off, race or abuse it at all. I'm very gentle with it. Considering the mileage, could I have blown a gasket so soon? It also feels like a lose of power or possibly the new carb needs some serious tweaking. Please don't tell me that's possibly the fate of my golden ship. What could be the problem?

I've taken it to a few mechanics and of course they all said blown head gasket. Well, you know what I'm thinking; they see my classic, think I have money and would lie to get it.

Besides, you guys here are the real experts and have gotten me out of rough places every time.

The following parts are new and been installed:
Radiator
Water pump
Hoses
Thermostat
Intake manifold
Carburetor

Thanks in advance

Was the engine overheating before the new parts were installed or were they installed in an attempt to correct the overheating ? You mentioned a new thermostat being installed - was it installed in the proper orientation ( with the spring facing the engine side and away from the hose going to the upper radiator inlet ) . If the overheating started only after the installation of the new thermostat , perhaps it is defective ? If the head gasket is the problem , you should see bubbles in the radiator with the engine running and the radiator cap removed . Have you checked that ? You mentioned the low mileage of your car - if it hasn't had the proper maintenance over the years ( including flushing the radiator and adding new fluid at the recommended intervals ), the head gaskets possibly are suffering from corrosion and that may have contributed to a failure in the ability to seal properly ?

Yes, the engine was overheating before changing all the new parts. I will certainly check the radiator for bubbles. The thermostat was installed correctly. Tried two different thermostats. Prior to the overheating I would drive it twice a month at the most.

Thanks